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AN  U  RES 


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FERTILISERS  AND  MANURES 


FERTILISERS  AND 
MANURES 


BY   A.    D.    HALL,    M.A.,    F.R.S. 

DIRECTOR   OF  THE    ROTHAMSTED   EXPERIMENTAL   STATION  ;    FOREIGN  MEMBER 
OF  THE    ROYAL   ACADEMY   OF   AGRICULTURE   IN   SWEDEN 


NEW  YORK 
E.  P.  BUTTON  AND  COMPANY 

1912 


DEDICATED    TO 

SIR  CHARLES   LAWES-WITTEWRONGE,  Baronet 

OF     ROTHAMSTED 

WHO    HAS    SHOWN    IN   OTHER     FIELDS 

THE   DISTINCTION    AND    IMAGINATION 

WHICH   MARKED    HIS   FATHER'S   WORK 

FOR   AGRICULTURE 


First  Edition     ......        June  1909 

Reprinted      .  ,  •  .  .        June  1910 

Reprinted      ......        May  1912 


PREFACE 

The  use  of  some  form  of  fertiliser  is  becoming  more 
and  more  a  mark  of  modern  agriculture.  Though  many 
farmers,  and  among  them  some  of  our  best,  still  pro- 
fess to  scorn  all  artificial  manures  and  pin  their  faith 
on  the  dung  made  by  their  stock,  they  none  the  less 
are  buying  the  elements  of  fertility — nitrogen,  phos- 
phoric acid,  and  potash — in  the  cakes  and  other  feeding 
stuffs  which  they  bring  from  some  outside  source  and  con- 
sume on  their  farms.  It  is  the  continual  introduction 
of  plant  food  from  outside  which  distinguishes  modern 
intensive  methods  of  cultivation  from  the  old  farming. 
Prior  to  a  period  which  roughly  coincides  with  the 
foundation  of  the  Royal  Agricultural  Society  of  Eng- 
land in  1838,  the  farmer,  living  on  the  inherent  capital 
of  the  soil,  was  forced  into  a  conservative  system  of 
cultivation,  which  by  restoring  in  the  dung  the  greater 
part  of  what  had  been  taken  from  the  soil  by  the  crops, 
would  reduce  the  losses  from  his  land  to  a  point  where 
they  would  be  more  or  less  balanced  by  the  natural  re- 
cuperative processes  at  work  in  the  soil.  In  consequence 
the  level  of  production  was  low,  and  it  was  the  discovery 
and  introduction  of  artificial  fertilisers  and  feeding 
stuffs — nitrate  of  soda,  guano,  the  phosphates,  cotton 
cake,  maize,  etc., — which  enabled  the  British  farmer  to 
raise  his  output  per  acre  by  at  least  50  per  cent, 
during  the  reign  of  the  late  Queen.     It  is  true  that  all 


vi  PREFACE 

intensive  farming  in  the  United  Kingdom  received  a 
great  set-back  in  the  'eighties  and  'nineties,  when  the 
continued  opening  up  of  new  areas  of  virgin  soil  and 
the  fall  in  freights  filled  the  country  with  corn  and  meat 
at  prices  below  our  cost  of  production  under  the  condi- 
tions then  prevailing,  because  declining  prices  cannot  be 
met  by  more  intensive  methods,  but  only  by  a  reduction 
in  the  expenditure.  However,  we  are  steadily  recover- 
ing from  that  position  :  the  supply  of  rich  virgin  soil  is 
not  without  a  limit  nor  are  its  riches  inexhaustible  ;  the 
cost  of  production  has  begun  to  rise  in  the  new 
countries,  already  we  see  the  American  farmer  is  in 
his  turn  being  compelled  to  resort  to  fertilisers;  and 
with  each  rise  in  prices  the  intensive  farmer  can 
recoup  himself  for  an  increased  outlay.  The  future, 
too,  lies  with  intensive  farming ;  every  year  the 
ratio  of  the  cultivable  land  to  the  population  of  the 
world  shrinks  ;  every  year  science  puts  fresh  resources  in 
the  hands  of  the  farmer.  In  the  United  Kingdom  for 
some  time  the  stream  may  still  run  backwards  and  the 
more  expensive  forms  of  arable  cultivation  continue  to 
be  replaced  by  grass  which  demands  no  outlay,  because 
as  long  as  ours  is  the  one  market  open  to  the  competi- 
tion of  all  other  countries  selling  agricultural  produce, 
prices  are  still  liable  to  such  wreckage  as  frightens  the 
home  grower  out  of  the  business ;  still,  in  the  end,  what- 
ever agriculture  survives  in  this  country  will  be  forced 
into  more  and  more  intensive  methods  by  the  increasing 
scarcity  of  the  land.  As  it  is,  the  specialist  farmers 
in  Great  Britain — the  potato  growers,  the  market 
gardeners,  the  hop  growers — have  reached  a  pitch  of 
cultivation  which  is  hardly  to  be  paralleled  elsewhere. 
Intensive  farming  implies  the  use  of  fertilisers ;  still 


PREFACE  vii 

more  it  implies,  or  should  imply,  skill  and  knowledge  in 
using  them. 

If  this  book  is  to  have  any  justification  for  its  exist- 
ence, it  will  be  by  helping  men  to  a  greater  skill  and 
knowledge  in  the  use  of  their  fertilisers  and  manure. 
There  is  no  lack  of  books  which  give  an  account  of 
the  origin  and  composition  of  fertilisers :  my  object  is 
rather  to  make  the  reader  understand  their  mode  of 
action  and  their  relation  to  particular  crops  and  soils. 
For  it  is  only  by  understanding  the  why  and  the  how 
that  a  farmer  can  properly  adjust  his  manures  to  his 
soil  and  his  style  of  farming ;  he  must  to  some  extent 
reason  the  scheme  out  for  himself,  he  cannot  simply 
be  told. 

The  scientific  man  is  always  being  asked  to  arrange 
his  experiments  to  demonstrate  the  best  way  of  grow- 
ing this  or  that  crop,  by  the  best  being  implied  the 
cheapest :  farming  visitors  to  Rothamsted  are  often 
inclined  to  suggest  that  the  plots,  if  interesting,  are 
not  "  practical."  After  sixty  years  of  work  they  rather 
expect  to  see  the  absolutely  cheapest  form  of  manur- 
ing each  crop  set  out  once  and  for  all.  But  in 
practical  farming  there  is  no  "best"  way  of  doing 
things ;  the  mere  fact  that  the  weather  of  the  coming 
season  is  unknown  makes  it  impossible  to  specify  the 
absolutely  right  course  either  in  cultivation  or  in  manur- 
ing. The  question  even  of  the  best  manure  for  a  given 
crop  is  complicated  by  the  manner  in  which  every  farm 
differs  somewhat  from  every  other,  not  merely  in  its  soil 
and  climate,  for  these  matter  less  than  is  commonly 
supposed,  but  in  its  object  and  management.  One 
man  aims  at  crops,  another  man  gets  his  money 
back   by   his   stock;    one   man    has   only   to   pay    15s. 


viii  '  PREFACE 

an  acre  rent,  another  has  to  get  twice  as  much  out  of 
his  land  before  he  touches  a  profit ;  one  man's  markets 
are  such  that  he  can  repay  himself  for  an  outlay  of  £^ 
an  acre  for  fertilisers  on  his  root  area,  whereas  another 
man  could  not  afford  20s. ;  no  one  recipe  can  be 
handed  out  to  suit  all  these  different  men. 

The  object,  then,  of  the  scientific  man  should  be  to 
lay  down  principles  which  the  practical  man  in  his 
turn  must  learn  to  apply  to  his  own  conditions ;  success 
is  only  possible  when  he  too  does  some  thinking. 
Furthermore,  the  object  of  experiments  should  be  to 
provide  knowledge  that  can  be  thus  applied  to  other 
conditions,  and  an  experiment  is  practical  just  in  so  far 
as  it  carries  out  its  avowed  object,  which  is  to  lead 
men  into  a  sound  and  fruitful  way  of  thinking  on 
the  question  at  issue. 

It  is  in  this  respect — the  elucidation  of  general 
principles — that  the  Rothamsted  experiments  have 
proved  so  exceedingly  valuable ;  though  initially  laid 
out  to  test  certain  definite  questions  about  the 
nutrition  of  crops,  the  answers  to  which  have  long 
since  been  absorbed  into  farming  practice,  the  design 
was  so  sound  and  the  continuity  of  the  record  has 
been  so  rigorously  maintained  that  the  results  now 
afford  an  instructive  commentary  on  the  whole 
range  of  the  science  of  crop  production.  We  have  by 
no  means  come  to  the  end  of  the  lessons  the  Rotham- 
sted experiments  can  teach :  every  new  theory,  each 
extension  of  our  knowledge,  finds  an  unsuspected 
criticism  or  an  illustration  in  the  records  that  are  still 
accumulating. 

I  have  in  consequence  throughout  this  book  used 
very   freely   the    results    of    the    Rothamsted    experi- 


PREFACE  ix 

merits;  and  if  the  conclusions  I  have  drawn  do  not 
always  square  with  popular  opinion,  I  have  none  the 
less  set  them  out  in  the  hope  that  other  experimenters 
would  thereby  be  led  to  check  or  revise  them. 
Agricultural  chemistry  is  still  cumbered  with  a  good 
many  a  priori  deductions  resting  upon  a  very  slender 
foundation — first  approximations  to  the  truth  which  fail 
because  they  do  not  take  all  the  factors  into  account ; 
it  is  about  many  of  these  opinions  that  the  Rothamsted 
results  suggest  scepticism. 

The  book  is  intended  for  farmers  and  for  the 
senior  students  and  teachers  in  our  agricultural  schools. 
I  have  therefore  kept  the  language  as  non-technical 
as  possible,  though  some  elementary  knowledge  of 
chemistry  has  to  be  assumed.  If  sometimes,  as  in 
Chapter  X.,  I  may  seem  to  have  gone  rather  far  in 
the  discussion  of  theoretical  questions,  it  is  in  pursuance 
of  my  main  idea  that  it  is  only  by  thinking  about  the 
rationale  of  manuring  we  can  arrive  at  right  practice. 
And  as  the  book  is  intended  for  those  who  are  using 
or  going  to  use  fertilisers,  I  have  not  troubled  to  say 
much  about  their  manufacture,  nor  have  I  dealt  at  all 
with  their  analysis :  these  are  both  technical  matters 
outside  the  business  of  the  farmer. 

I  have  meant  this  to  be  a  companion  to  my  book, 
The  Soil ;  they  are  both  written  for  the  same  audience, 
and  on  similar  lines.  I  hope  later  to  complete  the  series 
by  a  third  book,  dealing  with  the  chemistry  of  the  grow- 
ing plant. 

A  good  deal  of  the  material  in  the  book  has  already 
been  utilised  and  in  part  published  in  a  course  of 
Cantor  Lectures  delivered  before  the  Society  of  Arts 
in    1906,   and   again    in  a  course  of  lectures  delivered 


X  PREFACE 

at  Cornell  University  to  the  Graduate  School  of 
Agriculture  of  the  United  States  Department  of  Agri- 
culture in  July  1908.  In  this  way,  much  of  the  sub- 
stance of  Chapters  II.,  III.,  IV.,  V.,  and  VI.  has  already 
been  printed  in  the  Journal  of  the  Society  of  Arts,  the 
greater  part  of  Chapter  VI I.  has  appeared  in  the 
Journal  of  the  Board  of  Agriculture,  and  Chapter  X., 
the  last  of  my  American  lectures,  was  printed  in 
Science. 

I  have  drawn  so  freely  upon  my  friends  for  informa- 
tion, that  it  seems  invidious  to  single  out  for  thanks 
some  more  than  others :  but  I  owe  much  to  Dr  E.  J. 
Russell  of  this  Laboratory,  who  has  read  and  criticised 
parts  of  the  text ;  to  Dr  J.  A.  Voelcker,  who  has  so 
often  placed  the  results  of  his  wide  experience  at  my 
disposal ;  to  Mr  H,  Voss  of  the  Anglo-Continental 
Guano  Co.,  and  to  Mr  T.  Elborough  of  the  Lawes 
Chemical  Manure  Co.,  who  have  furnished  me  with 
many  facts  and  figures  respecting  the  trade  in  ferti- 
lisers ;  and  once  again,  to  Mr  G.  T.  Dunkley  of  the 
Rothamsted  Laboratory,  who  has  been  indefatigable  in 
verifying  references  and  in  securing  the  accuracy  of  the 
many  figures  and  tables  the  book  contains. 

A.   D.    HALL. 

The  Rothamsted  Experimental  Station, 
Harpenden,  December  1908. 


CONTENTS 

CHAPTER  I 

INTRODUCTORY 

Early  Notices  of  Manures  and  Manuring — The  Growth 
of  the  Theory  of  Nutrition  of  Plants — Priestley,  de 
Saussure,  Boussingault,  Liebig,  Lawes  and  Gilbert, 
Hellriegel  and  Wilfarth — The  Introduction  of  Com- 
mercial Fertilisers — General  Outline  of  the  Process  of 
Nutrition  of  Plants — The  Constituents  of  the  Soil — Mode 
of  Entry  of  Food  into  the  Plant — Nature  and  Function 
of  a  Fertiliser  .  .... 


CHAPTER  n 

FERTILISERS   CONTAINING   NITROGEN 

The  Importance  of  Nitrogen — Evidence  that  Plants  cannot 
utilise  the  Free  Nitrogen  of  the  Atmosphere — Ammonia 
and  Nitric  Acid  in  the  Atmosphere — Origin  of  the 
World's  Stock  of  Combined  Nitrogen — Nitrogen-fixing 
Bacteria — Fixation  of  Atmospheric  Nitrogen  to  form 
Calcium  Cyanamide — Fixation  of  Atmospheric  Nitrogen 
in  the  Electric  Arc  ;  Manufacture  of  Nitrate  of  Lime — 
Nitrate  of  Soda :  Nature  and  Origin — Properties  of 
Nitrate  of  Soda  :  Use  as  a  Fertiliser — Value  of  the  Soda 
Base — Injurious  Effects  of  Nitrate  of  Soda  upon  the 
Texture  of  the  Soil — Sulphate  of  Ammonia :  Sources 
and  Production — Changes  undergone  by  Sulphate  of 
Ammonia  in  the  Soil — Acidity  of  Soil  induced  by 
Sulphate  of  Ammonia — Relative  Value  of  Nitrate  of 
Soda  and  Sulphate  of  Ammonia — Other  Nitrogenous 
Fertilisers :  Soot,  Shoddy,  Fur  and  Feather  Waste, 
Hoofs  and  Horns — Slow  Action  of  such  Manures — 
Seaweed  .  .  .  .  .  -25 


xii  CONTENTS 

CHAPTER   III 

THE   FUNCTION    AND   COMPARATIVE   VALUE   OF 
NITROGENOUS   MANURES 

Nitrogen  promotes  the  Vegetative  Activity  of  the  Plant —  p^<^" 
Growth  proportional  to  Nitrogen  Supply — With  Excess 
of  Nitrogen  Maturity  is  deferred  and  the  Proportion  of 
Straw  to  Grain  is  increased — Variation  of  Composition 
of  Crop  with  Nitrogen  Supply — Susceptibility  of  Plants 
to  Disease  when  supplied  with  Excess  of  Nitrogen — 
Crops  requiring  Large  Quantities  of  Nitrogen — Relative 
Availability  of  Nitrogenous  Manures — Nitrate  of  Soda 
V.  Sulphate  of  Ammonia — Question  to  be  decided  by 
the  Nature  of  the  Soil — Residues  left  by  the  Different 
Nitrogenous  Manures  —  Greater  Value  attached  by 
Farmers  to  Manures  containing  Nitrogen  in  Organic 
Combination  .  .  .  .  .  .      yj 

CHAPTER   IV 

PHOSPHATIC    MANURES 

The  Phosphates  of  Calcium — The  Early  Use  of  Bones  as 
Manure — Preparation  of  Bone  Meal  and  Steamed  Bone 
Flour — Dissolved  Bones  and  Bone  Compounds — The 
Discovery  of  Mineral  Phosphates,  Coprolites,  Phos- 
phorite, Phosphatic  Guanos,  Rock  Phosphates — The 
Invention  of  Superphosphate,  Lawes  and  Liebig — The 
Manufacture  of  Superphosphate — -The  Manufacture  of 
Basic  Slag — Nature  of  the  Phosphoric  Acid  Compounds 
in  Basic  Slag,  their  Solubility  in  Dilute  Acid  Solutions — 
Basic  Superphosphate  —  Wiborg  Phosphate  —  Wolter 
Phosphate     .......     103 

CHAPTER  V 

THE    FUNCTION    AND    USE    OF    PHOSPHATIC 
FERTILISERS 

Ripening  Effect  of  Phosphoric  Acid — Most  manifest  in  wet 
Seasons— Effect  of  Phosphoric  Acid  in  stimulating  the 
Formation  of  Roots  and  Adventitiotis  Shoots — Associa- 
tion of  Phosphoric  Acid  with  the  Intake  of  Nitrogen  by  the 
Plant — Solvents  to  determine  the  Relative  Availability 
of  Phosphatic  Fertilisers — Relative  Value  of  Phosphatic 
Fertilisers  determined  by  the  Soil — Soils  appropriate  to 


CONTENTS  xili 

Superphosphate — Fate   of    Superphosphate   applied    to    ^''^^ 
the    Soil — Soils    appropriate    to    Basic    Slag — Neutral 
Phosphatic   Manures   for    Light    Soils — Comparison   of 
Bone  Meal  with  other  Phosphatic  Fertilisers        .  .136 


CHAPTER  VI 

THE    POTASSIC    FERTILISERS 

Early  Use  of  Wood  Ashes — The  Stassfurt  Deposits — Manu- 
facture and  Composition  of  Commercial  Potash  Fertilisers 
— The  Retention  of  Potash  by  the  Soil — The  Function 
of  Potash  in  the  Nutrition  of  the  Plant — Dependence  of 
Carbohydrate  Formation  upon  Potash,  as  illustrated  in 
the  Barley  and  Mangold  Crops — The  Action  of  Nitrate 
of  Soda  upon  Insoluble  Potash  Compounds  in  the  Soil — 
Potash  Fertilisers  as  promoting  the  Growth  of  Legu- 
minous Plants  —  Effects  of  Potash  Starvation  upon 
Vegetation — Potash  as  a  Preventive  of  Fungoid  Disease 
— Potash  as  prolonging  the  Growth  of  the  Plant — 
Destruction  of  the  Tilth  of  Clay  Soils  by  Potash  Salts — 
Soils  deficient  in  Potash     .  .  .  ,  .158 

CHAPTER  Vn 

FARMYARD    MANURE 

Variable  Composition  of  Farmyard  Manure — The  Fate  of  the 
Constituents  of  Food  during  Digestion  and  Excretion — 
Composition  of  Urine  and  Fasces  of  Farm  Animals — 
Fermentation  Changes  taking  place  during  the  Making 
of  Dung — The  Breakdown  of  the  Nitrogenous  Bodies 
and  of  the  Carbohydrates — Gases  found  in  the  Dunghill 
— Losses  of  Nitrogen  during  the  making  of  Farmyard 
Manure — Preservatives  used  to  minimise  the  Losses 
during  Dung-making — Composition  of  Farmyard  Manure 
—  Cake-fed  v.  Ordinary  Manure  —  Long  and  Short 
Manure — London  Dung — The  Value  of  Fresh  Manure — 
The  Fertilising  Value  of  Farmyard  Manure — Recovery 
of  its  Nitrogen  in  the  Crop — Long  Duration  of  the  Action 
of  Farmyard  Manure — Farmyard  Manure  as  a  Carrier 
of  Weeds  or  Disease — The  Physical  Effects  of  Farmyard 
Manure  upon  the  Soil — The  Improvement  in  Texture 
and  Water- retaining  Power — Value  of  Farmyard  Manure 
as  a  Mulch  on  Grass  Land — Farmyard  Manure  best 
utilised  for  the  Root  Crop  or  Grass  Land — Value  of 
Farmyard  Manure  :  Cost  of  making  One  Ton      .  .     178 


«V  CONTENTS 


CHAPTER   VIII 

PERUVIAN    GUANO    AND    OTHER    MIXED 
FERTILISERS 

Origin  of  the  Deposits  of  Guano — Variation  in  Composition  p*^°« 
with  Age — Compounds  of  Nitrogen  present  in  Peruvian 
Guano  —  Ichaboe  and  Damaraland  Guanos  —  Fish 
Guano — Meat  Guano — Dried  Blood — Greaves — Rape 
Dust  and  other  Cake  Residues — Manures  derived  from 
Faecal  Matter — Sewage  Sludges    ....     229 

CHAPTER  IX 

MATERIALS    OF    INDIRECT    FERTILISING   VALUE 

Lime — Early  Use  of  Lime — White  and  Grey  Limes — Lime 
Ashes — Marl — Chalk — Ground  Limestone — Indications 
of  the  Lack  of  Lime  in  the  Soil — Action  of  Lime  upon 
the  Soil — Improvement  of  Texture — Promotion  of  the 
Oxidation  of  nitrogenous  Residues  in  the  Soil — Increase 
in  the  Availability  of  Phosphoric  Acid  and  Potash — 
General  Action  of  Soluble  Salts  on  the  Soil — Gas 
Lime  —  Gypsum  —  Salt  —  Sulphate  and  Carbonate  of 
Magnesia — Sulphate  of  Iron  ;  Supposed  Connection  of 
Iron  in  the  Soil  with  the  Colour  of  Fruit  and  Flowers — 
Manganese  Salts — Silicates — Green  Manuring — Folding 
Catch  Crops  on  the  Land   .....     249 

CHAPTER  X 

THEORIES    OF    FERTILISER    ACTION 

Liebig's  Ash  Theory — Part  played  by  the  Soil  in  the  Nutrition 
of  the  Crop — Ville's  Theory  of  Dominants — Liebig's 
Law  of  the  Minimum — Law  of  diminishing  Returns — 
Limiting  Factors  in  Plant  Growth — Is  the  Composition 
of  the  Soil  Water  unaffected  by  Fertilisers  ? — Attack  of 
the  Plant's  Roots  upon  Insoluble  Fertilisers — The  Part 
played  by  Carbon  Dioxide  in  the  Soil — Excretion  of 
Toxic  Substances  from  Plant  Roots — Rotations  as  a 
Substitute  for  Fertilisers — Unexplained  Factors  in  the 
Nutrition  Problem  ......     276 


CONTENTS  XV 

CHAPTER  XI 

SYSTEMS    OF    MANURING    CROPS 

High  and  Low  Farming — Fertilising  Constituents  removed  P'^o" 
in  Meat  and  Corn — Losses  of  Nitrogen  increased  when 
Land  is  in  high  Condition — Manures  for  Wheat — 
Barley:  Importance  of  Quality  —  Oats  —  Root  Crops: 
Swedes,  Mangolds,  Potatoes — Importance  of  Farmyard 
Manure  for  Root  Crops — Leguminous  Crops  :  Beans, 
Clover,  Lucerne,  Sainfoin — Value  of  Potassic  Fertilisers — 
Grass  Land — Effect  of  Manures  in  changing  the  Botanical 
Character  of  the  Herbage — Land  laid  up  for  Hay — 
Manures  for  Poor  Pastures  —  Hops  —  Fruit  —  Garden 
Manures  —  Manures  for  Tropical  and  Semi-Tropical 
Crops  :  Sugar  Cane,  Tobacco,  Cotton,  Tea  .  .     300 

CHAPTER  Xn 

THE    VALUATION    AND    PURCHASE    OF 
FERTILISERS 

Valuation  on  the  Unit  System — The  current  Market  Price 
of  the  Unit  of  Nitrogen — Phosphate  of  Lime  and  Potash 
— Variations  in  Unit  Values  due  to  Market  Fluctuations 
—  Valuation  of  Fertilisers  before  Purchase  —  The 
Fertilisers  and  Feeding  Stuffs  Act  ;  Obligations  of  the 
Vendor — Sampling  Consignments  of  Fertilisers — Mixed 
V.  Unmixed  Fertilisers — Incompatibles — Residues  of 
Fertilisers  after  the  Growth  of  one  or  more  Crops — 
Valuation  of  unexhausted  Residues  derived  from  the 
Consumption  of  purchased  Feeding  Stuffs  .  .     340 

CHAPTER  XHI 

THE    CONDUCT    OF    EXPERIMENTS    WITH 
FERTILISERS 

Magnitude  of  Experimental  Error  mvolved  in  Field  Experi- 
ments— Choice  of  Land  for  Field  Experiments — Size 
and  Shape  of  Plots — Machines  for  sowing  Fertilisers — 
Should  Farmers  conduct  Experiments  upon  their  own 
Land?  .......     359 

Index .    .078 


LIST   OF    ILLUSTRATIONS 

FIO.  FACE   PAGE 

1.  Water  Cultures  of  Barley     .  .  .  .  .17 

2.  Deflocculating  Action  of  Nitrate  of  Soda  on  Clay  Soils    .         55 

3.  Curves    showing    the    effect    of    Phosphoric    Acid    in 

hastening  the  formation  of  Grain  of  Barley,  and  the 
Migration  of  Nitrogen  to  the  Grain      .  .  .137 

4.  Effect  of  Excess  of  Nitrogen,  with  and  v/ithout  Potash,  on 

the  Leaves  of  Mangolds  .  .  .  .174 

5.  Relation  between  Cost  of  Production  and  Returns  with 

varying  quantities  of  Manure     ....       284 

6.  Diagrammatic    Section    of    Manure    Distributor — Seed 

Drill  Type  ■■■■■■       373 

7.  Diagrammatic    Section    of    Manure     Distributor,     with 

Revolving  Drum  Feed  .....       373 

8.  Diagrammatic  Section  of  Manure  Distributor — Endless 

Chain  Feed  Type  .....       374 


9.  Broadcast    Manure    Sower   with    Revolving    Discs    for 
Distribution        »  .  .  t  .  t 


374 


FERTILISERS    AND    MANURES 


CHAPTER   I 

INTRODUCTORY 

Early  Notices  of  Manures  and  Manuring — History  of  the  Theory 
of  Nutrition  of  Plants — Priestley,  de  Saussure,  BoussingaulL 
Liebig,  Lawes  and  Gilbert,  Hellriegel  and  Wilfarth — The 
Introduction  of  Commercial  Fertilisers — General  Outline  of 
the  Process  of  Nutrition  of  Plants — The  Constituents  of  the 
Soil — Mode  of  Entry  of  Food  into  the  Plant — Nature  and 
Function  of  a  Fertiliser. 

The  word  "  manure,"  when  first  met  with  in  English, 
possessed  a  much  wider  significance  than  it  does 
to-day.  Of  the  same  origin  as  manoeuvre,  it  meant, 
primarily,  to  work  by  hand,  and  it  is  used  in  that  sense 
by  Defoe  in  Robinson  Crusoe — "  The  land  which  I  had 
manured  or  dug";  but  it  also  took  on  the  extended 
meaning  of  any  process  or  material  by  which  the  land 
could  be  ameliorated.  In  the  seventeenth  and  early 
eighteenth  centuries  this  latter  sense  alone  began  to 
prevail ;  agricultural  writers  enumerated  chalk,  lime, 
marl,  burnt  clay,  etc.,  as  manures,  and  began  to  speak 
of  the  operations  of  cultivation  as  tillages  or  husbandry  ; 
and  more  recently  the  tendency  has  been  to  restrict 
the  employment  of  the  term  even  further,  confining 
it  to  the  natural  substances  possessing  a  direct  fertilising 

A 


2  INTRODUCTORY  [chap. 

value.  Farmyard  manure  is  the  typical  "manure"; 
marl  or  chalk  would  no  longer  be  regarded  as  manure, 
because  they  do  not  feed  the  plant  directly;  while 
substances  like  basic  slag  or  nitrate  of  soda,  which 
simply  supply  one  or  other  element  in  the  nutrition 
of  a  plant,  should  be  termed  "  fertilisers  "  rather  than 
artificial  manures.  The  distinction  is  not,  however, 
very  clearly  drawn,  and  manure  and  fertiliser  are  gener- 
ally and  unconsciously  used  as  interchangeable  terms, 
as  indeed  they  will  be  in  this  book. 

It  is  impossible  to  assign  a  period  to  the  discovery 
of  the  fertilising  properties  of  the  excrement  of  animals : 
agriculture  must  be  almost  coeval  with  the  human  race  ; 
and  that  tissue  of  experience  and  observation  which 
reaches  us  as  the  tradition  of  farming — the  stock-in- 
trade  of  the  practical  man — began  to  form  long  before 
letters  existed  by  which  it  could  be  recorded.  At  any 
rate,  when  in  Rom. an  times  we  began  to  get  some 
record  of  agricultural  practices,  we  find  that  not  only 
was  the  value  of  dung  recognised,  but  that  the  virtues 
of  certain  other  manures,  such  as  marl,  had  been 
established.  Even  the  fertilising  effect  of  a  crop  of 
vetches  or  lupins  upon  the  succeeding  wheat  crop  was 
sufficiently  well  known  to  be  related,  not  only  by  pro- 
fessed agricultural  writers  like  Varro  and  Columella,  but 
also  by  a  poet  like  Virgil.  But  to  whatever  point  the 
knowledge  of  manures  had  reached  in  the  time  of  the 
Romans,  for  a  long  time  it  made  no  further  advances 
and  bade  fair  to  be  utterly  lost  with  the  irruption  of 
the  barbarians.  When  the  new  peoples  emerge  again 
in  Europe,  after  the  great  movements  of  the  races,  we 
mostly  find  them  practising  the  Germanic  common 
field  system  of  agriculture,  with  its  rotation  of  wheat, 
beans  or  barley,  and  fallow,  followed  up  by  general 
grazing  over  the  whole  area — a  system  which  lends  no 


I.]  EARLY  niSTORY  OF  MANURES  3 

encouragement  to  the  use  of  substances  like  manures 
for  the  improvement  of  the  land. 

Doubtless  the  old  traditions  did  not  perish  in  the 
Romance  countries,  but  as  before  were  handed  down 
from  one  generation  to  another  ;  as  long  as  corn  and 
wine  continued  to  be  cultivated  the  immemorial  pre- 
cepts concerning  their  management  would  linger  about 
the  country  side  and  be  treasured  in  the  memories  of 
the  workers  in  the  fields.  But  during  the  Dark  Ages 
this  kind  of  knowledge  sank  below  the  level  of  what- 
ever literature  was  being  written ;  it  had  to  diffuse 
slowly  from  the  remains  of  Roman  civilisation  among 
the  invading  peoples,  and  it  is  only  by  chance  that  we 
get  any  record  of  what  the  countryman  did  or  thought. 
In  many  English  tenures  we  find  that  the  flocks  of  the 
tenants  had  to  be  folded  on  the  lord's  land  at  night, 
the  manure  thus  brought  being  one  of  his  most  valued 
privileges ;  while  in  Walter  de  Henley's  Husbandrie,  the 
great  mediaeval  treatise  on  the  duties  of  a  land  agent, 
we  find  instructions  for  the  preservation  of  dung  by 
the  use  of  litter  and  marl.  The  manure  thus  obtained 
was  to  be  stored  in  a  heap  and  preferably  applied  to 
sandy  land.  From  mediaeval  times  also  we  derive  such 
maxims  as  the  Flemish  proverb, 

Point  de  fourrage,  point  des  betail. 
Point  des  betail,  point  de  fumier, 
Point  de  fumier,  point  de  fourrage. 

When,  with  the  general  resurrection  of  learning  at  the 
Renaissance,  we  once  more  get  books  on  agriculture, 
we  find  that  either  old  tradition  or  the  experience  of 
men  of  an  enquiring  turn  of  mind,  who  had  been 
trying  all  sorts  of  things  on  their  land,  had  already 
built  up  a  certain  knowledge  of  manures  and  manuring. 
The  value  of  marl  and  chalk,  of  woollen  rags  and  ashes, 
was   certainly  known   in   the  sixteenth  century;   men 


4  INTRODUCTORY  [chap. 

had  even  begun  to  reason  a  little  on  the  mode  of  action 
of  manures.  For  example,  Bernard  Palissy  the  potter, 
in  his  Recepte  Veritable,  published  in  1563,  not  only 
recommends  the  use  of  marl  and  lime,  but  can  assign  a 
reason  for  the  value  of  ashes,  and  shows  that  the  rich- 
ness of  farmyard  manure  resides  in  the  portion  soluble 
in  water : — "  Et  ainsi  la  paille  estant  bruslee  dedans 
le  champ,  elle  seruira  d'autant  de  fumier,  parce  que 
elle  laissera  la  mesme  substance  qu'ell  auoit  attiree 
de  la  terre  ...  ; "  and  again,  "  au  lieu  ou  ledit  pilot  de 
fumier  aura  repose  quelque  temps,  ils  n'y  laisseront 
rien  dudit  fumier,  avis  le  jetteront  deca  et  dela,  mais 
au  lieu  ou  il  aura  repose  quelque  temps,  tu  verras 
qu'apres  que  la  ble  qui  aura  este  seme  sera  grand,  il 
sera  in  cest  endroit  plus  espes,  plus  haut,  plus  verd  et 
plus  droit.  Par  la  tu  peux  aisement  cognoistre  que  ce 
n'est  pas  le  fumier  qui  a  cause  cela,  car  le  labourer  le 
jette  autre  part ;  mais  c'est  que  quand  ledit  fumier  estoit 
au  champ  par  pilots,  les  pluyes  qui  sont  suruenues,  ont 
passe  a  travers  des  dits  pilots,  et  sont  descendu  a  travers 
du  fumier  jusqu'a  la  terre,  et  en  passant,  ont  dissout  et 
emporte  certains  parties  du  sol  qui  estoit  audit  fumier." 

If,  then,  by  the  sixteenth  century  we  find  written 
evidence  of  the  knowledge  of  the  fertilising  properties 
not  only  of  dung  but  of  other  waste  substances,  we 
may  safely  push  back  the  original  discovery  of  the 
properties  of  these  bodies  to  a  much  more  remote  epoch, 
if  such  a  term  as  discovery  can  properly  be  applied. 
Just  as  happens  to-day,  this  or  that  man  tried  an 
experiment  or  noticed  the  result  of  an  accident  which 
caused  him  to  report  well  of  the  action  of  some  sub- 
stance on  his  crops ;  his  opinion  would  often  be 
mistaken  and  often,  again,  it  would  be  forgotten  ;  but 
occasionally  it  would  be  repeated  and  find  confirmation, 
until  it  acquired  the  wide  circulation  and  staying  power 


I.]  SCIENCE  AND  TRADITION  5 

of  a  farming  tradition  and  passed  more  or  less  into  the 
common  routine.  Even  at  the  present  time  there  are 
many  beliefs  and  practices  more  or  less  current  among 
farmers,  which  science  has  neither  verified  nor  disproved, 
and  which  may  either  be  examples  of  sound  observation 
or  only  imperfect  generalisations.  Such  opinions 
require  to  be  examined  with  the  utmost  care  and  open- 
mindedness,  for  even  when  correct  they  are  of  no  final 
use  to  agriculture  until  they  have  been  explained  and 
absorbed  into  the  general  stream  of  scientific  knowledge. 
The  value  of  many  fertilisers  must  have  been  observed 
and  lost  sight  of  over  and  over  again,  because  of  the 
lack  of  any  general  theory  to  serve  as  a  touchstone  and 
discriminate  between  the  true  and  the  false  reports. 
So,  despite  the  experience  that  was  accumulating 
respecting  the  fertilising  value  of  this  or  that  substance, 
no  real  progress  towards  a  theory  of  manuring  was 
made  until  the  close  of  the  eighteenth  and  the 
beginning  of  the  nineteenth  century. 

Before  the  development  of  a  science  of  chemistry  it 
was  naturally  impossible  to  form  any  idea  of  how  a 
plant  came  to  grow ;  while  the  nature  of  the  plant 
itself,  of  the  air,  water,  and  earth  were  equally  unknown, 
no  correct  opinion  could  be  reached  as  to  how  the  latter 
gave  rise  to  the  former.  In  spite  of  Palissy's  very 
sound  conclusions  as  to  the  salts  plants  draw  from  the 
ground,  Van  Helmont  described  an  experiment  to 
show  that  a  tree  is  made  out  of  water  alone.  Jethro 
Tull,  arguing  from  his  hoeing  experiments,  concluded 
that  manures  were  unnecessary :  for  the  soil,  if  only 
stirred  up  enough  and  exposed  to  the  air,  will  provide 
all  that  the  plant  requires.  Even  so  late  as  1810  we  find 
Thaer  writing  that  there  is  no  doubt  that  the  fallow 
absorbs  or  attracts  the  fertilising  properties  of  the 
atmosphere. 


6  INTRODUCTORY  [chap. 

The  true  theory  of  the  nutrition  of  the  plant  begins 
very  soon  after  the  discovery  of  the  composition  of  the 
air.  "Thus,  Priestley  observed  that  plants  possessed 
the  faculty  of  purifying  air  vitiated  by  combustion  or 
by  the  respiration  of  animals ;  and  he  having  discovered 
oxygen,  it  was  found  that  the  bubbles  which  Bonnet 
had  shown  to  be  emitted  from  the  surface  of  leaves 
immersed  in  water  consisted  chiefly  of  that  gas.  Ingen- 
housz  demonstrated  that  the  action  of  light  was  essential 
to  the  development  of  these  phenomena,  and  Sennebier 
proved  that  the  oxygen  evolved  resulted  from  the 
decomposition  of  the  carbonic  acid  taken  up." 

Following  up  these  results,  de  Saussure  demonstrated 
with  as  much  quantitative  accuracy  as  was  then  possible 
that  the  oxygen  which  was  split  off  by  the  leaf  was 
contained  in  the  carbonic  acid,  and  that  the  gain  in 
weight  of  the  plant  was  practically  represented  by 
its  carbon ;  combined  with  the  elements  of  water  to 
make  up  such  carbo-hydrates  as  sugar  and  starch. 
De  Saussure  further  arrived  at  very  clear  ideas  as  to 
the  source  and  value  of  the  ash  constituents  of 
plants :  the  nitrogen,  which  he  also  pointed  out 
as  an  invariable  constituent  of  plants,  he  considered 
to  be  either  derived  from  the  ammonia  in  the 
atmosphere  or  the  organic  matters  in  the  soil.  Sir 
Humphrey  Davy,  in  his  lectures  before  the  Board 
of  Agriculture  from  1802  to  1813,  practically  adopted 
de  Saussure's  views,  and  emphasised  the  importance 
of  the  ash  constituents,  which  could  come  neither 
from  the  air  nor  water,  as  he  yet  thought  it  necessary 
to  demonstrate. 

Though  Davy  made  no  advances  towards  ascertain- 
ing the  relative  importance  of  these  substances,  and 
was  by  no  means  certain  that  the  plant  derived  all 
its  carbon    from    the    atmosphere,     his     lectures    did 


I.]  THEORIES  OF  PLANT  NUTRITION  7 

much  to  pave  the  way  for  the  adoption  of  a  sound 
theory. 

Thaer,  about  the  same  period,  was  still  attributing  the 
chief  share  in  the  nutrition  of  the  plant  to  the  organic 
juices,  or,  as  we  should  say,  to  the  humus  in  the  soil, 
which  substance  he  showed  to  contain  hydrogen,  nitrogen, 
sulphur,  and  phosphorus.  Though  knowledge  of  the 
composition  of  plants,  soils,  and  manures  continued  to 
accumulate,  as  seen  in  the  work  of  Sprengel  and 
Schubler,  the  next  step  forward  was  due  to  Boussingault, 
who  was  the  first  man  to  undertake  field  experiments  on 
a  practical  scale.  Farming  his  own  land  at  Bechelbronne, 
Alsace,  from  1834  onwards,  he  systematically  weighed 
crops  and  manure  and  analysed  both  so  as  to  obtain  a 
balance-sheet  showing  the  quantities  of  carbon  and  nitro- 
gen added  in  manure  and  removed  in  the  crops.  He 
thus  in  1838  demonstrated  on  a  working  scale  the 
enormous  amounts  of  carbon  w^hich  are  assimilated  by 
the  plant  from  the  atmosphere — far  greater  quantities 
than  the  humus  in  the  soil  could  continue  to  supply. 
Boussingault's  experiments  led  him  to  conclude  that  the 
plant  derives  its  nitrogen  from  the  soil,  though  he  also 
showed  that  in  certain  rotations  more  nitrogen  is 
removed  in  the  crop  than  is  supplied  in  the  manure. 

But  it  is  to  the  great  Liebig  that  we  must  attribute 
the  chief  impulse  which  agricultural  chemistry  has 
received ;  though  he  made  little  original  contribution 
himself  to  the  theory,  adopting  in  the  main  the  con- 
clusions that  arose  from  the  work  of  Priestley,  Ingen- 
housz,  Sennebier,  and  de  Saussure,  he  was  the  man  who 
drove  home  to  the  minds,  both  of  scientific  men  and  of 
farmers,  the  true  theory  of  plant  nutrition. 

In  his  report  to  the  British  Association,  published 
in  1840,  and  his  Chemical  Letters ,  he  laid  down  the 
general    principle    that   the   carbon   compounds,  which 


8  INTRODUCTORY  [chap. 

constitute  more  than  95  per  cent,  of  the  dry  matter  of 
the  plant,  are  derived  by  the  plant  from  the  atmosphere, 
and  that  if  the  plant  be  supplied  with  the  2  per  cent, 
or  so  of  mineral  constituents  which  are  found  in  its  ash, 
it  will  then  draw  upon  the  atmosphere  for  all  the  other 
materials  the  crop  ultimately  contains. 

Coming  at  a  time  when  much  intellectual  interest 
was  directed  towards  agriculture,  and  backed  by  his  great 
scientific  reputation  and  his  commanding  personality, 
Liebig's  views  aroused  instant  and  general  attention ; 
they  became  the  foundation  both  of  practical  experi- 
ment and  scientific  research,  and  were  the  starting-point 
of  a  controversy  the  echoes  of  which  are  but  now  dying 
down.  In  several  respects  Liebig's  views  required 
modification ;  he  seemed  to  consider  all  the  ash  con- 
stituents were  of  equal  importance,  and  even  that  one 
base  like  soda  could  replace  any  similar  one  like  potash ; 
he  regarded  the  composition  of  the  plant's  ash  as  deter- 
mining its  proper  fertiliser — a  point  which  will  be  con- 
sidered later ;  and  he  misapprehended  the  part  played 
by  nitrogen  compounds  in  manuring.  At  that  time, 
owing  to  imperfections  in  the  methods  of  analysis,  very 
exaggerated  ideas  were  current  as  to  the  amount  of 
ammonia  naturally  present  in  the  atmosphere :  the 
rain  was  believed  to  bring  down  30  or  40  lb.  per  acre 
per  annum  of  combined  nitrogen  instead  of  the  3  or  4  lb., 
which  we  now  know  to  be  contributed  to  the  soil,  and 
to  this  source  Liebig  was  disposed  to  look  for  the 
nitrogen  in  the  plant.  He  stated  that  manures  contain- 
ing nitrogen  certainly  stimulated  growth,  because  they 
fermented  and  increased  the  proportion  of  ammonia  in 
the  air  round  the  plant ;  but  in  the  main  nitrogenous 
manures  were  unnecessary,  for  full  crops  could  be  grown 
if  only  the  constituents  removed  in  the  ash  were  annually 
returned  to  the  soil. 


I.]  ROTHAMSTED  9 

In  particular,  these  views  on  the  nutrition  of  plants 
and  the  part  played  by  the  nitrogenous  nianures,  did 
not  commend  themselves  to  John  Bennet  Lawes,  a 
young  Hertfordshire  landlord  who  had  recently  come 
into  possession  of  the  family  estate  of  Rothamsted,  near 
St  Albans,  and  had  already  begun  to  try  manurial 
experiments  on  a  small  scale.  In  1843  the  experiments 
took  more  systematic  form  and  Lawes  obtained  the 
services  of  Joseph  Henry  Gilbert,  a  chemist  who  had 
worked  under  Liebig  at  Giessen,  to  conduct  them, 
thus  inaugurating  the  field  trials  which  have  continued 
without  a  break  to  the  present  day.  The  immediate 
result  of  the  Rothamsted  experiments  was  to  demon- 
strate the  necessity  of  a  supply  of  combined  nitrogen, 
the  yield  being  in  fact  roughly  proportional  to  the 
amount  of  combined  nitrogen  added  as  manure.  If 
only  the  mineral  constituents  of  the  ash  were  supplied, 
the  crop  fell  away  rapidly  as  soon  as  the  reserves  of  active 
nitrogen  in  the  soil  had  become  exhausted.  Lawes, 
Gilbert,  and  Pugh  further  repeated,  with  great  exacti- 
tude, a  series  of  laboratory  experiments  initiated  by 
Boussingault,  and  demonstrated  that  the  ordinary  plants 
of  the  farm  were  incapable  of  utilising  the  free  nitrogen 
of  the  atmosphere,  but  only  took  up  nitrogen  in  a 
combined  form  from  the  soil  or  the  manure.  Lawes 
and  Gilbert  were  fiercely  attacked  by  Liebig ;  but  as  far 
as  his  views  can  be  extracted  from  his  writings,  there 
was  no  very  great  difference  between  the  opinions  held 
by  the  rival  parties.  Liebig  laid  the  chief  stress  on 
the  need  for  the  mineral  manures,  whereas  the  latter 
investigators  were  more  concerned  to  demonstrate  the 
importance  of  nitrogen.  Liebig  also  seems  to  have 
thought  that  the  leafy  crops,  like  clover  or  roots — the 
so-called  restorative  crops — could  gather  nitrogen  from 
the    atmosphere    and    dispense    with    any   supply    in 


lo  INTRODUCTORY  [chap. 

manure.  But  in  addition  to  establishing  the  value  of 
nitrogenous  manures,  the  Rothamsted  experiments  also 
settled  in  a  practical  fashion  the  question  of  which  of 
the  ash  constituents  were  indispensable  to  the  plant 
and  were  necessary  constituents  of  a  complete  manure. 
The  fundamental  necessity  of  phosphoric  acid  and 
potash,  and  the  non-essential  nature  of  soda,  magnesia, 
and  silica  as  manure  constituents  were  soon  established, 
and  the  experiments  began  at  once  to  bear  fruit  in  the 
way  the  various  artificial  manures,  then  being  discovered 
and  put  on  the  market,  were  utilised  by  farmers. 
Contemporaneously  the  methods  of  pot  cultures  in  weak 
solutions  of  known  salts  were  evolved,  and  in  the  hands 
of  Boussingault,  Knop,  Stohmann,  and  others,  demon- 
strated with  all  the  precision  of  a  laboratory  process 
that  of  the  elements  found  in  the  plant,  only  compounds 
of  nitrogen,  phosphoric  and  sulphuric  acids  among 
acids,  and  potash  and  lime  with  a  trace  of  iron  among 
bases,  are  absolutely  essential  to  the  nutrition  of  the 
plant. 

There  was,  however,  still  one  point  which  remained 
somewhat  unintelligible — the  gain  in  combined  nitrogen 
which  seemed  to  take  place  when  certain  crops  of  the 
leguminous  order  were  grown.  Cases  were  recorded 
where  more  nitrogen  was  found  in  the  crop  than  was 
supplied  in  the  manure,  and  yet  the  soil  on  which  the 
crop  had  been  grown  itself  showed  an  increase  of 
nitrogen. 

Boussingault,  in  his  earliest  investigations,  had  shown 
that  in  certain  rotations  which  included  clover  or  lucerne 
more  nitrogen  was  removed  in  the  crop  than  had  been 
supplied  in  the  manure,  and  many  of  the  Rothamsted 
results  could  only  be  explained  on  the  assumption  that 
the  roots  of  such  crops  ranged  exceptionally  deep  and 
drew  upon  stores  of  subsoil  nitrogen  unavailable  for  other 


I.]  NITROGEN  AND  VEGETATION  ii 

plants,  thus  leaving  the  upper  soil  the  richer  for  their 
prowth,  since  the  roots  and  stubble,  in  which  this  subsoil 
nitrogen  has  been  accumulated,  decay  near  the  surface. 
It  was  not  until  1886  that  these  difficulties  were  cleared 
up  by  the  discovery  of  Hellriegel  and  Wilfarth  that 
leguminous  plants  do  fix  the  atmospheric  nitrogen  by 
the  help  of  certain  bacteria  living  in  symbiosis  upon  the 
root  of  the  leguminous  plant.  The  leguminous  plant, 
however,  will  also  feed  upon  combined  nitrogen  in  the 
soil  like  any  other  plant,  and  the  failure  of  Lawes  and 
Gilbert  to  detect  any  nitrogen  fixation  in  their  labora- 
tory experiments  with  beans  and  clover,  was  due  to  the 
great  care  to  shut  out  any  intrusion  of  foreign  matter 
during  the  experiments,  thus  preventing  the  leguminous 
plants  from  becoming  inoculated  with  the  bacteria 
causing  fixation.  In  a  measure,  the  discovery  of 
Hellriegel  and  Wilfarth,  which  has  formed  the  starting- 
point  of  much  further  research,  may  be  taken  to  have 
justified  some  of  Liebig's  arguments,  although  the 
mechanism  by  which  the  nitrogen  fixation  is  brought 
about — by  bacteria  living  in  concert  with  the  higher 
plant — would  have  been  entirely  foreign  to  his  way  of 
looking  at  things,  just  as  it  was  to  Lawes  and  Gilbert, 
who  thus  unhappily  missed  the  clue  which  would  have 
rendered  intelligible  many  of  their  results. 

It  has  been  already  indicated  how  impossible  it  is  to 
recover  the  date  of  the  original  discovery  of  the 
fertilising  value  of  the  substances  we  now  call  artificial 
manures ;  only  by  an  occasional  allusion  in  the  older 
books  can  we  find  that  particular  materials  were  in 
common  use  at  the  period  of  the  writer.  Blithe's 
English  Improver,  published  in  1653,  mentions  the 
value  of  rags,  wool,  marrow  bones  or  fish  bones,  horn 
shavings,  soot,  and  wood  ashes ;  and  Evelyn,  writing  a 
few  years  later,  adds  also   blood,  hair,  feathers,  hoofs, 


12  INTRODUCTORY  [chap. 

skin,  fish,  malt  dust,  and  meal  of  decayed  corn,  so  that 
a  knowledge  of  the  value  of  these  materials  must  have 
been  widespread. 

William  Ellis,  a  Hertfordshire  farmer  who  wrote  in 
1732,  enumerates  a  long  list  of  "hand  manures,"  the 
use  of  which  he  regarded  as  characteristic  of  Hertford- 
shire farming  in  his  day.  These  include  soot,  wood 
ashes,  woollen  rags,  horn  shavings,  hoofs,  hair,  coney 
clippings,  oil  cake,  and  malt  dust ;  and  the  regular  part 
they  evidently  played  in  the  farming  of  that  district 
show  that  they  must  have  been  known  and  used  for  a 
long  time  previous  to  Ellis's  writings.  Throughout  the 
eighteenth  century  we  hear  of  the  same  materials,  and 
also  of  bones,  which  Ellis  does  not  mention,  though 
their  value  is  stated  by  several  of  the  seventeenth 
century  writers.  Early  in  the  nineteenth  century  we 
begin  to  hear  of  guano  from  Peru,  though  the  first 
importation  did  not  take  place  until  1840. 

The  importation  of  nitrate  of  soda  from  Chile  had 
begun  a  year  or  two  before  ;  its  value  as  manure  was 
for  a  time  in  doubt,  though  as  early  as  1669  Sir  Kenelm 
Digby  had  recounted  an  experiment  to  show  how  much 
barley  plants  were  benefited  by  watering  with  a  weak 
solution  of  nitre,  and  Evelyn  in  1675  ^^^  written:  "I 
firmly  believe  that  were  saltpetre  to  be  obtained  in 
plenty,  we  should  need  but  few  other  composts  to 
meliorate  our  ground." 

The  employment  of  ammoniacal  salts  seems  to  have 
begun  entirely  upon  theoretical  grounds ;  de  Saussure 
had  attributed  the  nitrogen  of  vegetation  to  the 
ammonia  in  the  atmosphere,  and  in  this  he* was 
followed  by  Liebig;  fortunately,  about  the  same  time, 
the  manufacture  of  coal-gas  gave  to  the  world  a  cheap 
source  of  ammonium  salts.  Lawes  had  already  been 
trying  them  before  Liebig's  paper  of  1840,  and  wher] 


I.]  INTRODUCTION  OF  ARTIFICIAL  FERTILISERS  13 

the  Rothamsted  experiments  were  definitely  started  in 
1843,  a  mixture  of  muriate  and  sulphate  of  ammonia 
became  their  standard  nitrogenous  manure. 

The  use  of  mineral  phosphates  as  manure  begins 
with  Lawes'  superphosphate  patents  in  1842,  although 
no  mineral  phosphates  were  available  on  a  large  scale 
until  Henslow's  discovery  of  the  coprolite  beds  of 
Cambridgeshire  in  1845,  soon  after  which  time  Lawes 
and  others  took  them  up  as  material  for  the  manu- 
facture of  superphosphates.  Putting  aside  the  various 
methods  adopted  for  the  utilisation  of  slaughter-house 
refuse,  etc.,  no  further  novel  manurial  substances  can  be 
said  to  have  been  introduced  until  the  development  of 
the  Stassfurt  potash  deposits,  which  began  about  i860, 
and  the  discovery  of  basic  slag  in  1879,  which  has  been 
followed  in  the  last  few  years  by  various  processes  for 
bringing  atmospheric  nitrogen  into  a  combined  form. 

Since  the  nutrition  of  the  plant  is  the  object  with 
which  all  manures  are  employed,  it  will  be  necessary 
at  the  outset  to  obtain  some  knowledge  of  how  a  plant 
feeds  under  the  simplest  possible  conditions  without 
any  of  the  disturbing  effects  introduced  by  the  many 
complex  processes  going  on  in  the  soil. 

If  we  take  any  living  plant  and  reduce  it  to  its 
elements,  we  find  but  a  small  range  of  substances ; 
water  forms  the  greatest  portion  of  the  plant,  the  rest 
is  almost  wholly  composed  of  compounds  of  carbon 
with  hydrogen  and  oxygen,  approximately  in  the 
proportions  which  make  up  water.  Of  the  dry  matter 
of  the  plant  at  least  half  is  carbon ;  oxygen  and  hydro- 
gen constitute  most  of  the  remainder;  then  a  certain 
restricted  number  of  other  elements  are  present  in  much 
smaller  quantities.  Nitrogen  constitutes  about  2  per 
cent,  of  the  dry  matter  ;  the  other  substances,  which  are 
found  in  the  ash  when  the  plant  is  burnt,  make  up  a 


14  INTRODUCTORY  [chap. 

further  2  per  cent,  or  so.  These  ash  constituents  com- 
prise sulphur,  phosphorus,  silicon,  and  chlorine,  among 
the  non-metals  ;  potassium,  sodium,  calcium,  magnesium, 
and  a  little  iron  and  manganese,  among  the  metals. 
Traces  of  other  metals  occur  from  time  to  time  in  the 
ashes  of  plants  growing  on  soils  which  happen  to 
contain  them,  but  they  are  unessential  and  may  in  this 
connection  be  neglected. 

Carbon,  then,  is  the  main  element  in  the  plant's 
economy,  and  we  know  that  it  is  obtained  by  the  plant 
from  the  carbonic  acid  in  the  atmosphere  through  the 
agency  of  the  living  cells  in  the  leaf,  which  contain 
green  chlorophyll.  The  carbonic  acid  is  taken  in 
through  the  small  openings  in  the  skin  of  the  leaf,  the 
stomata  ;  it  is  decomposed  by  the  chlorophyll-containing 
cells,  and  the  carbon  is  retained  in  combination  with 
the  elements  of  water,  so  that  it  is  first  identifiable  as 
sugar  and  then  as  starch ;  at  the  same  time  oxygen  is 
returned  to  the  atmosphere.  This  decomposition  is 
one  that  necessitates  an  external  supply  of  energy, 
which  is  found  to  be  derived  from  the  light  incident 
upon  the  leaf,  the  process  stopping  in  darkness,  and 
for  low  illuminations  becoming  proportional  to  the 
amount  of  light  falling  upon  the  leaf. 

The  conditions  affecting  this  process  of  photo- 
synthesis— the  fundamental  reaction  of  the  whole  plant- 
world — have  been  subjected  to  considerable  examina- 
tion of  late.  In  the  method  adopted  by  H.  T.  Brown, 
the  leaf,  which  may  still  be  attached  to  the  plant,  is 
enclosed  in  a  flat  air-tight  box  with  glass  sides,  through 
which  sweeps  a  rapid  but  measured  current  of  air.  The 
issuing  air  which  has  passed  over  the  leaf  is  led  into 
an  apparatus  for  the  determination  of  the  carbonic 
acid  (and,  if  need  be,  of  the  water)  it  contains ;  at  the 
same    time    a    parallel    experiment   without    the    leaf 


!•] 


ASSIMILATION 


J5 


measures  the  proportion  of  carbonic  acid  and  water 
in  the  incoming  air.  Thus  the  amount  of  carbonic  acid 
absorbed,  and  therefore  decomposed,  in  a  given  time 
by  a  leaf,  whose  area  can  be  afterwards  measured,  is 
directly  determined,  and  such  factors  as  illumination  and 
temperature  can  be  varied  at  will.  The  energetics  of 
the  process  have  been  worked  out  by  Brown  and 
Escombe,  from  whose  paper  the  following  examples 
have  been  selected  : — 

Table  I.— Utilisation  of  the  Energy  incident  on  a  Green 
Leaf.    (Brown  and  Escombe.) 


E 

E 

nergy  in  Calories  per  sq.  cm.  of  Leaf, 

'C 

c    O 

per  minute. 

i^ 

s-2 

£  c 

-c  ^ 

-c 

^m 

?  oJ 

0  rf 

3  >, 

t.  5 

^^^. 

Plant. 

"S  ^ 

■^  ^ 

•JS  J 

■^  '^ 

'5     •— 

-^  rt  S 

^  o 

"S  5 

?S| 

^0 

5|| 

8 

S  5... 
5  ~ 
§1 

[-.  >-  ^ 
^^  0  ►-' 

S-r  5 

e;  cS  0 

c.c. 

grnis. 

Polygonum 

3-7£8 

I -054 

0-1942 

0-1256 

0-0031 

O-IO4I 

0-0184 

(Juno  19) 

Tropoeolum 

I -498 

0-141 

0-0889 

0-0622 

0-0012 

0-OI39 

0-0471 

(September  4) 

Helianthus 

2-134 

1-259 

0-2569 

0-1762 

o-ooi  7 

0.1243 

0-0502 

(August  7) 

These  experiments  show  that  the  leaf  of  a  plant 
is  not  to  be  regarded  as  a  very  efficient  machine  for 
the  decomposition  of  carbonic  acid,  since  in  no  case  was 
more  than  i-66  per  cent,  of  the  total  energy  incident 
on  the  leaf  used  for  photo-synthesis,  so  that  even  dull, 
diffuse  daylight  can  amply  provide  a  growing  plant 
with  the  energy  it  wants  for  assimilation.  The  process, 
however,  is  limited  by  many  factors,  any  one  of  which 
may  fix  a  minimum  rate  at  which  assimilation  will  take 


1 6  INTRODUCTORY  [chaP. 

place,  however  favourable  the  other  conditions  are. 
Temperature,  the  supply  of  water,  the  proportion  of 
carbonic  acid  in  the  air,  the  number  and  area  of  the 
stomatic  openings,  are  all  limiting  factors  of  this  kind, 
as  also  is  the  supply  of  other  nutriment  to  the  plant. 

Though  the  compounds  of  carbon  with  hydrogen 
and  oxygen  make  up  so  much  of  the  solid  matter  of 
the  plant,  the  remaining  substances,  comparatively 
small  in  amount  as  they  are,  are  still  all-important  to 
the  process  of  growth.  The  part  they  respectively  play 
and  their  mode  of  entry  can  best  be  illustrated  by  the 
method  of  water  cultures,  of  which  Fig.  i  shows  an 
example.  By  this  method  the  roots  of  young  seedling 
plants  are  just  allowed  to  dip  into  a  large  jar  of  water 
in  which  salts  of  the  elements  found  in  the  plant  are 
dissolved.  A  complete  solution  might  be  made  up  as 
follows : — 

Grammes  per  litre. 

Calcium  Nitrate 07 

Potassium  Phosphate o-6 

Potassium  Chloride     .....      o-8 
Magnesium  Sulphate 0-3 

with  a  trace  of  ferric  chloride. 

This  will  contain  all  the  elements,  except  silicon, 
normally  found  in  plant  ashes,  and  under  such  condi- 
tions the  plant  will  grow  and  go  through  its  whole 
cycle  of  life,  assimilating  freely,  producing  large  quanti- 
ties of  dry  matter,  setting  flowers,  and  ripening  healthy 
seed.  Certain  precautions  have  to  be  taken,  but  if  the 
right  conditions  are  assured,  the  growth  of  a  plant  in 
a  water  culture  is  perfectly  normal,  and  may  be  taken, 
as  far  as  the  plant  is  concerned,  as  representing  the 
course  of  its  nutrition  in  the  field.  The  advantage  of 
the  method  lies  in  the  fact  that  it  is  possible  to  vary 
the  composition  of  the  nutrient  solution  by  omitting  in 
turn  from   successive  jars   each   of  the   salts   used   in 


Fig.  I.— Water  Cultures  of  Barley. 

1.  Complete  Manure.  4.  No  Potash. 

2.  No  Nitrogen.  5.  No  Lime. 

3.  No  Phosphoric  Acid.  6.  No  Magnesia. 


'To  face  vaae  17. 


I.]  NUTRITION  OF  THE  PLANT  17 

making  up  the  complete  solution,  thus  obtaining  media 
for  the  plant  containing  no  nitrogen,  no  phosphorus,  no 
potassium,  etc.,  the  other  constituents  found  in  the 
plant  being  present  in  each  case.  The  result  of  one 
such  series  of  experiments  is  shown  in  Fig.  i,  which 
illustrates  that  when,  e.g.,  nitrates  are  omitted  from  the 
culture  solution,  the  plant  is  quite  unable  to  grow 
after  it  has  used  up  the  material  in  the  seed,  however 
freely  it  may  have  been  provided  with  potassium, 
magnesium,  etc  The  net  result  of  such  experiments, 
in  agreement  with  the  one  shown  in  the  photograph, 
is  that  a  plant  must  obtain  by  means  of  its  root 
nitrogen  in  combination,  phosphorus,  sulphur,  potas- 
sium, magnesium,  calcium,  and  a  little  iron — all  of 
which  constituents  are  indispensable  to  the  growth 
of  the  plant  and  cannot  be  omitted  from  the 
culture  solutions.  Sodium,  silicon,  and  probably  chlo- 
rine, though  invariable  constituents  of  the  ash,  are 
not  necessary  and  can  be  dispensed  with.  From 
these  water  culture  experiments  we  arrive,  then,  at 
the  conclusion  that  the  plant  must  draw  certain 
elements,  in  quantities  which  are  small  compared 
with  the  weight  of  the  crop  but  are  nevertheless 
indispensable,  out  of  the  soil  by  means  of  its  roots,  the 
rest  of  the  plant  being  built  up  from  air  and  water. 
These  water  culture  experiments  may  also  be  made 
to  lead  to  another  conclusion,  which  we  first  of  all 
owe  to  de  Saussure — that  the  nutrient  substances 
must  first  of  all  be  dissolved  or  capable  of  going  into 
solution  before  they  can  feed  the  plant.  The  growing 
plant  contains  80  per  cent,  or  more  of  water,  but  this 
amount  bears  but  a  small  proportion  to  the  total 
quantity  of  water  which  passes  through  the  plant 
during  the  whole  period  of  growth.  There  exists, 
in   fact,   a  continual    •'  transpiration   current "   through 


1 8  INTRODUCTORY  [chap. 

the  plant,  of  water  which  enters  by  the  root  hairs  and 
is  eventually  evaporated  from  the  leaves  and  other 
growing  surfaces  of  the  plant.  It  has  been  shown 
that  under  the  normal  conditions  the  plant  transpires 
from  200  to  500  pounds  of  water  for  every  pound  of 
dry  matter  that  is  simultaneously  produced  ;  the  lower 
number  being  nearer  the  factor  prevailing  in  our  humid 
atmosphere,  and  the  higher  one  holding  for  drier  coun- 
tries. With  this  water  enter  the  nutrient  constituents 
of  the  soil  and  of  fertilisers  applied  to  it ;  but  the 
process  by  which  they  enter  is  rather  more  complex 
than  one  of  the  simple  intake  of  a  solution. 

The  passage  of  the  dissolved  substances  into  the 
plant  takes  place  by  the  purely  physical  process 
of  osmosis,  the  walls  of  the  root  hairs  (which  con- 
sist of  single  elongated  cells)  acting  as  membranes 
through  which  water  or  salts  will  pass  independently, 
according  to  the  relative  concentration  of  the  solu- 
tions inside  or  outside  the  cell.  Should  the  cell  sap 
be  more  concentrated  than  the  soil  water  outside, 
pure  water  will  pass  through  the  wall  until  a  certain 
osmotic  pressure  (causing  turgor  in  the  plant)  is 
reached,  which  varies  with  the  concentration.  If,  on 
the  contrary,  the  soil  water  became  more  concentrated 
than  the  cell  sap,  water  will  leave  the  cell,  the  plant 
will  become  flaccid,  and  even  die  if  the  withdrawal  of 
water  be  too  great.  It  is  in  this  way  that  plants 
become  "  scorched "  or  "  burnt "  by  too  concentrated 
solutions  of  any  kind  of  soluble  salts,  such  as  are  formed 
when  a  little  soluble  manure,  salt,  etc.,  falls  upon  the 
surface  of  a  leaf 

Not  only  will  water  pass  in  or  out  of  the  cell,  but 
an  equilibrium  will  be  attained  between  the  cell  sap  and 
the  external  soil  water  for  each  constituent  present  in 
the  latter.    If,  for  example,  sodium  or  potassium  chlorides 


I.]  ENTR  Y  OF  PLANT  FOOD  19 

be  present  in  solution  in  the  external  soil  water,  both 
will  continue  to  diffuse  through  the  cell  wall  until  their 
respective  concentrations  are  the  same  within  and 
without  the  cell.  If  now  the  potassium  compounds 
be  withdrawn  from  the  solution  within  the  cell  by 
the  living  protoplasm  in  order  to  take  part  in  the 
various  vital  processes  requiring  potassium,  there 
will  be  a  fresh  influx  of  potassium  until  the  old  equi- 
librium within  and  without  is  restored.  It  is  in  this 
way  that  the  apparent  selective  action  of  a  plant 
takes  place ;  as  a  rule,  sodium  compounds  are  more 
abundant  in  soil  water  than  salts  of  potassium,  yet 
the  ash  of  the  plant  will  be  found  much  richer  in 
potassium  than  in  sodium.  Similarly,  again,  the  ash 
of  any  particular  plant  will  maintain  a  fairly  constant 
composition  although  grown  on  soils  of  widely  differing 
character.  The  selective  power  resides  in  the  living 
cells  themselves ;  all  substances  dissolved  in  the  soil 
water  diffuse  through  the  walls  of  the  root  hairs  into 
the  plant,  but  will  not  continue  to  accumulate  therein 
unless  they  are  utilised  and  withdrawn  from  solution 
by  the  protoplasm. 

Further,  it  is  not  necessary  to  consider  that  the 
plant  takes  up  the  various  salts  presented  to  it  as 
wholes ;  the  process  of  diffusion  until  equilibrium  is 
attained,  of  withdrawal  by  the  protoplasm  and  con- 
sequent renewal  of  the  process  of  diffusion,  takes 
place  for  each  acid  or  base  independently  of  the 
others.  As  a  rule,  a  plant  growing  in  a  nutrient 
medium  containing  nitrates  as  sources  of  nitrogen,  will 
withdraw  an  excess  of  acid  and  render  the  solution 
alkaline,  but  cases  also  occur  when  the  medium 
becomes  acid  during  growth  because  the  plant  takes 
more  base  than  acid.  According  to  modern  views  of 
solution,  we  must  regard  the  soil  water  as  a   highly 


20 


INTRODUCTORY 


[CHAP. 


ionised  solution,  and  each  particular  kind  of  ion 
establishes  its  own  conditions  of  equilibrium  within 
and  without  the  cell. 

The  soil,  however,  is  not  to  be  regarded  merely  as 
an  inert  medium  to  anchor  the  plant  and  convey  the 
manure  to  it  when  convenient,  but  is  itself  an  enormous 
potential  reserve  of  plant  food. 

We  may  take,  by  way  of  an  example,  the 
Rothamsted  soil.  On  the  one  hand,  it  is  neither 
richer  nor  poorer  than  the  majority  of  British  soils 
and  has  no  abnormal  characteristics,  so  that  it  repre- 
sents a  very  fair  average  type ;  on  the  other  hand, 
there  is  no  other  soil  about  which  so  much  knowledge 
has  been  accumulated. 

Table  II.— Analysis  of  the  Soil  of  Broadbalk  Field, 
Rothamsted,  Unmanured  for  50  Years. 


Per  cent. 

Lb.  per 
Acre. 

Loss  on  ignition 

Containing  Carbon  .... 

„           Nitrogen 
Matter  soluble  in  Hydrochloric  Acid    . 
Containing  Soda      .... 

„           Potash   .... 

„           Magnesia 

„           Lime      .... 

„           Alumina 

„           Oxide  of  Iron 

„           Phosphoric  Acid    . 

„           Sulphuric  Acid 

,,            Carbonic  Acid 
Undissolved  Siliceous  Matter 

4-20 

12-53 
83-27 

0-89 

O-IO 

o-o6 

0-27 

0-36 
2-49 
4-49 
3-40 

0>II 

0-05 
I -30 

22,250 
2,500 

1,500 
6,750 
9,000 

62,250 
112,250 

85,000 
2,750 
1,250 

32,500 

The  accompanying  analysis  shows,  as  usual,  that 
the  greater  part  of  the  soil  consists  of  insoluble 
siliceous  matter,  of  which  no  account  need  be  taken ; 
there  is,  further,  a  certain  amount  of  organic  material, 
important  as  containing  a  store  of  nitrogen  which  may 


I.]  AMOUNT  OF  PLANT  FOOD  IN  SOIL  21 

eventually  reach  the  plant.  In  addition,  we  have 
various  salts  going  into  solution  in  the  acids  used 
for  the  analytical  process,  and  these  include  pre- 
cisely the  substances  that  have  already  been  indi- 
cated as  constituents  of  the  ash  of  plants — amongst 
metals,  calcium,  magnesium,  potassium,  sodium,  with 
iron  and  aluminium  in  quite  disproportionate  amounts; 
sulphuric  and  phosphoric  acids,  chlorine  and  silica 
supply  the  non-metals.  Read  as  percentages  some 
of  these  amounts  seem  small  enough,  but  they  repre- 
sent enormous  quantities  of  material  in  the  soil,  as 
will  be  realised  when  they  are  correlated  with  the 
fact  that  the  layer  of  soil  at  Rothamsted,  nine  inches 
deep,  which  is  taken  for  analysis,  weighs,  over  the  area 
of  one  acre,  rather  more  than  two  and  a  half  million 
pounds.  Translating,  then,  the  percentages  into  pounds 
per  acre,  o-i  per  cent,  of  nitrogen  becomes  2500  lb., 
o-ii  of  phosphoric  acid  becomes  2750  lb.,  and  the 
potash  rises  to  6750  lb. ;  also,  these  quantities  are  in 
the  surface  soil  only,  without  considering  the  lower 
layers  into  which  the  plant  roots  penetrate  freely. 
A  comparison  of  the  materials  in  the  soil  with  those 
taken  away  by  ordinary  crops  at  once  leads  to  results 
which  seem  paradoxical ;  the  stock  of  plant  food  in 
the  soil  is  so  much  greater  than  any  requirements 
of  the  crop  that  further  additions  of  the  same  stuff 
in  the  shape  of  fertilisers  would  seem  to  be  needless. 
The  accompanying  table  (III.)  shows  the  amounts 
of  various  materials  per  acre  which  are  on  the  average 
drawn  from  the  soil  by  various  crops  at  Rothamsted. 

Roughly  speaking,  an  average  soil  contains  enough 
plant  food  for  a  hundred  full  crops,  yet  without  fresh 
additions  of  plant  food  as  manures  the  production  will 
shrink  in  a  very  few  years  to  one-third  or  one-fourth  of 
the  average   full   crop.     Once,  however,  the  yield  has 


22 


INTRODUCTORY 


[CKAP' 


reached  this  lower  level,  it  will  remain  for  an  indefinite 
period  comparatively  stationary,  affected  only  by  the 
fluctuations  due  to  season.  At  Rothamsted,  for  example, 
wheat  has  now  been  grown  year  after  year  on  the  same 
land  for  sixty-five  seasons,  and  one  plot  has  received 
no  manure  throughout  the  whole  period.     In  the  first 

Table  III, — Soil  Constituents  contained  in  Average 
Crops. 


Wheat. 

Barley. 

Swedes. 

Mangolds. 

Hay. 

Tons. 

Tons. 

Tons. 

Tons. 

Tons. 

Crop 

2-2 

2-0 

I6-I 

30-1 

1-5 

Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

Nitrogen   . 

50 

49 

98 

149 

49 

Soda 

2-6 

5.0 

32-0 

II8-7 

9-2 

Potash 

28-8 

35-7 

79-7 

30O-7 

50-9 

Magnesia  . 

7-1 

6.9 

9-2 

42-5 

14-4 

Lime      .    . 

9-2 

9-2 

42.4 

42-9 

32-1 

Phosphoric  Acid 

2I-I 

20.7 

21-7 

£2-9 

12.3 

Sulphur     . 

7.8 

6-1 

17-8 

14-0 

5-7 

Chlorine    . 

2-5 

4-1 

I5-I 

83-1 

14.6 

Silica 

96.9 

68-6 

6.7 

17-9 

56-9 

few  years  the  crop  declined  steadily,  but  since  then  little 
or  no  further  drop  has  been  seen.  The  yield  remains 
at  about  I2|  bushels  per  acre  for  each  successive  ten 
years'  average,  and  has  considerably  overtopped  that 
amount  during  recent  favourable  seasons.  This  yield, 
however,  of  12  J  bushels  of  corn  per  acre,  is  only  about 
a  third  of  that  obtained  on  the  adjacent  plots  receiving 
manure  every  year  during  the  same  period. 

These  facts  lead  to  a  new  point  of  view :  it  is  not 
merely  the  amount  of  this  or  that  plant  food  present  in 
the  soil  which  must  be  taken  into  account  but  also 
their  mode  of  combination.  The  material  may  be 
present  in  the  soil  and  soluble  in  the  acid  used  for 
analysis,  but  yet  may  be  beyond  the  reach  of  the  plant 


I.]       DORMANT  AND  AVAILABLE  PLANT  FOOD      23 

in  a  locked-up  or  dormant  condition.  The  plant  can 
only  obtain  substances  which  have  been  previously  dis- 
solved in  the  water  contained  by  soils  in  the  field,  hence 
plant  food  in  the  soil  is  only  available  for  the  plant  in 
so  far  as  it  can  pass  into  solution. 

Accepting,  then,  the  fact  that  the  soil  contains  a  vast 
store  of  all  the  elements  necessary  to  its  nutrition  but 
in  forms  of  low  availability,  it  remains  to  ascertain 
which  of  the  substances  are  normally  likely  to  fall  below 
the  current  requirements  of  the  crop.  This  is  a  ques- 
tion that,  can  only  be  solved  by  field  experiments,  and 
though  the  answer  will  vary  with  each  crop  and  each 
soil  yet  certain  general  principles  at  once  become 
evident  and  upon  them  the  whole  idea  of  a  fertiliser  is 
based.  For  example,  field  experiments  at  once  show 
that  certain  elements  indispensable  to  the  plant,  as  seen 
from  water  culture  experiments,  need  not  be  supplied 
to  the  crop  in  the  field,  since  the  soil  is  practically 
always  able  to  provide  a  sufficiency.  Calcium, 
magnesium,  iron,  sulphur,  chlorine,  and  silicon  fall  into 
this  class  ;  to  judge  by  field  experiments  alone  there 
are  only  three  elements  required  for  the  nutrition  of  the 
crop — nitrogen,  phosphorus,  and  potassium — and  this 
means  that  soils  can  usually  supply  the  elements 
necessary  to  the  plant  in  sufficient  quantities,  except  in 
these  three  cases.  Fertilisers,  then,  are  designed  to 
supply  deficiencies  in  the  soil,  and  for  all  practical 
purposes  are  to  be  regarded  as  consisting  of  compounds 
of  nitrogen,  phosphoric  acid,  and  potash,  either  singly  or 
together.  They  may  also  contain  magnesia,  lime,  or 
sulphuric  acid,  but  these,  though  equally  necessary  to 
the  plant,  are  not  counted,  since  the  unaided  soil  may 
be  trusted  to  furnish  the  crop  with  them. 

To  summarise  the  position  we  have  reached :  a 
fertiliser   must  contain  one  or  more  of  the  three  sub- 


24  INTRODUCTORY  [chap.  1. 

stances,  nitrogen,  phosphoric  acid,  and  potash,  which 
alone  among  the  various  elements  necessary  to  the 
nutrition  of  the  plant  cannot  be  supplied  by  cultivated 
soils  in  amounts  sufficient  for  profitable  crop  production. 
The  soils  do  contain  these  substances  in  comparatively 
enormous  quantities,  but  the  distinguishing  feature  of  a 
fertiliser  which  makes  it  effective  when  supplied  in 
quantities  comparable  with  those  removed  by  the  crop, 
is  its  "  availability." 

A  distinction  is  often  drawn  between  natural  and 
artificial  manures ;  properly  speaking,  the  latter  should 
include  only  such  materials  as  are  the  results  of  some 
manufacturing  process,  e.g.,  sulphate  of  ammonia,  super- 
phosphate and  basic  slag.  But  practically  speaking,  any 
concentrated  fertiliser  that  is  brought  on  to  the  farm  in 
bags,  though  its  origin  be  as  natural  as  the  sea  birds* 
excrement  constituting  "guano,"  or  the  ground  seeds 
known  as  "  rape  dust,"  gets  called  an  artificial  manure, 
in  contradistinction  to  the  farmyard  manure  which  is 
the  normal  product  of  the  farm.  In  all  the  published 
reports  dealing  with  the  Rothamsted  experiments  it  has 
been  customary  to  distinguish  such  substances  as  are 
found  in  the  ash  of  a  plant — the  phosphates,  the  sul- 
phates, and  chlorides  of  the  alkalis  or  alkaline  earths — 
as  "mineral  manures";  the  compounds  containing  nitro- 
gen are  regarded  as  distinct,  since  they  are  ultimately  of 
organic  origin,  even  when  they  consist  of  such  obviously 
mineral  substances  as  nitrate  of  soda  or  chloride  of 
ammonia.  The  term  "cinereals"  has  also  been  pro- 
posed in  place  of  mineral  manures  or  ash  constituents ; 
none  of  the  terms  are  satisfactory,  but  since  attempts 
at  corrected  terminology  only  result  in  increased  con- 
fusion, the  term  "  mineral  manures,"  however  imperfect, 
will  continue  to  be  used  throughout  this  book  for 
fertilising  substances  containing  no  nitrogen. 


CHAPTER  II 

FERTILISERS   CONTAINING   NITROGEN 

The  Importance  of  Nitrogen — Evidence  that  Plants  cannot  utilise 
the  Free  Nitrogen  of  the  Atmosphere — Ammonia  and  Nitric 
Acid  in  the  Atmosphere — Origin  of  the  World's  Stock  of 
Combined  Nitrogen — Nitrogen-fixing  Bacteria — Fixation  of 
Atmospheric  Nitrogen  to  form  Calcium  Cyanamide — Fixation 
of  Atmospheric  Nitrogen  in  the  Electric  Arc  ;  Manufacture  of 
Nitrate  of  Lime — Nitrate  of  Soda:  Nature  and  Origin — 
Properties  of  Nitrate  of  Soda  :  Use  as  a  Fertiliser — Value  of 
the  Soda  Base — Injurious  Effects  of  Nitrate  of  Soda  upon  the 
Texture  of  the  Soil — Sulphate  of  Ammonia  :  Sources  and 
Production — Changes  undergone  by  Sulphate  of  Ammonia  in 
the  Soil — Acidity  of  Soil  induced  by  Sulphate  of  Ammonia — 
Relative  Value  of  Nitrate  of  Soda  and  Sulphate  of  Ammonia 
— Other  Nitrogenous  Fertilisers :  Soot,  Shoddy,  Fur  and 
Feather  Waste,  Hoofs  and  Horns — Slow  Action  of  such 
Manures — Seaweed. 

Amongst  the  elements  of  the  nutrition  of  the  plant 
the  first  place  must  be  given  to  nitrogen  ;  not  only  does 
it  cost  more  per  pound  to  the  farmer  than  do  the  other 
necessary  elements,  but  as  a  fertiliser  applied  to  ordinary 
soils  it  seems  to  have  a  more  direct  and  immediate 
effect  upon  the  plant ;  furthermore,  it  differs  from  the 
others  in  that  plants  live  habitually  in  contact  with  a 
vast  unusable  store  of  it.  Since  plants  live  in  an 
atmosphere  four-fifths  of  which  consists  of  elementary 
nitrogen,  it  is  perhaps  necessary  to  justify  a  little  the 


26    FERTILISERS  CONTAINING  NITROGEN    [chap.  ll. 

Statement  made  in  the  previous  chapter,  that  they  only 
obtain  the  nitrogen  they  require  in  a  combined  form  by 
means  of  their  roots.  The  form  that  the  demonstration 
has  taken  may  be  seen  in  the  water  culture  experiment 
which  has  already  been  illustrated ;  in  the  absence  of 
combined  nitrogen,  the  development  of  the  plant  is  very 
small.  The  same  is  true  for  cultures  in  sand,  which  re- 
produce more  closely  the  natural  conditions,  and  many 
experiments  have  been  performed  with  the  greatest 
care  with  plants  thus  growing  in  artificial  soils  supplied 
with  a  known  amount  of  nitrogen.  When  the  plants 
have  come  to  the  full  term  of  their  growth,  the  nitrogen 
they  contain  is  found  to  be  exactly  balanced  by  the 
amount  of  the  same  element  which  has  been  removed 
from  the  soil.  Among  these  experiments,  a  most 
elaborate  series  were  carried  out  at  Rothamsted  in 
1857-58,  and  were  generally  regarded  as  definitely 
settling  the  question  against  the  fixation  of  nitrogen 
by  the  plant  itself 

The  experiments  were  made  with  wheat,  barley, 
oats,  clover,  beans,  peas,  and  buckwheat,  and  the  trials 
were  repeated,  in  the  one  case  with  no  manure  in  the 
pots,  and  in  the  other  with  the  supply  of  a  small 
quantity  of  sulphate  of  ammonia.  The  soils  employed 
were  made  up  from  either  ignited  pumice  or  ignited 
soil,  and  the  glass  shades  under  which  the  plants  were 
grown  rested  in  the  groove  of  a  stoneware  vessel,  mercury 
being  used  as  a  lute.  The  air,  previously  passed 
through  sulphuric  acid  and  sodium  carbonate  solution 
and  washed,  was  forced  into  the  apparatus,  so  as  to 
always  maintain  a  greater  pressure  inside  than  out, 
thus  minimising  all  danger  of  unwashed  air  leaking  in ; 
carbonic  acid  was  also  introduced  as  required.  Under 
these  rigorous  conditions  the  following  results  were 
obtained : — 


Tari.k  IV.— Summary  of  the  Results  of  Exf'eriments  made  at 
rotuamsted  to  determine  whether  plants  assimilate 
Free  Nitrogen. 


Nitroireu. — Giaui. 


Ill  Seed 

and 
Manure 
if  any. 


lu 

Plants, 

Pot,  and 

Soil. 


Gain  or 
Loss. 


WITH  NO  COJIBINED  NITROGEN  SUPPLIED  BEYOND  THAT 
IN  THE  SEED  SOWN. 


Gramineae 


Leguminosas 


Other  Plants  . 


1857- 


1858 


1858J 


1857 


1858 


Wheat       . 

Barley 

Barley 

o-oo8o 
0-0056 
0-0056 

0-0072 
0-0072 

0-C082 

Wheat       . 

0-0078 

0-0081 

Barley 
Oats  . 

0-0057 
0-0063 

0-0058 
0-0056 

Wheat       . 
Oats  . 

0-0078 
0-0064 

0-0078 
0-0063 

Beans 

0-0796 

0-0791 

Beans 
Peas  . 

0-0750 
0-01S8 

0-0757 
00167 

Buckwheat 

0-0200 

0-0182 

-  o  oooS 
+  0-0016 
+  0-0026 

+  0-0003 
+  0-0001 

-  0-0007 


-0-000 1 
-0-000; 


+  0-0007 
-0-0021 


-0-0018 


0-90 
1-29 
1-46 

1-04 
1-02 
0-89 

I -00 
0-98 

0-99 

I -01 

089 

0-91 


with  combined  nitrogen  SUPPLIED. 


Leguminosse  -[ 

Other  Plants . 


1857- 


1858 


1858J 

i858{ 

18:8 

iS;8 


Wheat 
Wheat 
Barley        , 
Barley        . 

Wheat        , 
P)arley 
Oats  . 

Wheat 
Barley 
Oats . 

Peas  . 
Clover 

Beans 
Buckwheat 


0-0329 

0-0383 

0-0329 

0-0331 

0-0326 

0-0328 

0-0268 

0-0337 

0-0548 

0-0536 

0-0496 

0-0404 

0-0312 

0-0216 

0-0268 

0.0274 

0-0257 

0-0242 

c-0260 

0-0198 

0-0227 

00211 

0-0712 

00665 

0-07 1 1 

0-0655 

0-030S 

0-0292 

+  0-0054 

+  0-0002 
+  0-0002 
+  0-0069 

-0-00I2 
-0-0032 
-0-0096 

+  0-0006 
-0-0015 
-  0-0062 

-o-ooi6 
-0-0047 

-0-0056 
-o-ooi6 


I-I6 

I -or 

I -01 
1-25 

o-qS 
o-i,4 
o-u^ 

1-02 

0-94 
0-76 

0-93 
0-93 

0-92 
0-95 


28        FERTILISERS  CONTAINING  NITROGEN     [chap. 

And  if  objection  be  made  that  such  plants  were 
enfeebled  by  the  unnatural  conditions,  so  that  they 
had  lost  their  power  to  bring  nitrogen  into  combina- 
tion— to  "  fix  "  it,  in  current  language — there  are  many 
other  types  of  experiment  which  render  such  criticism 
invalid.  For  example,  Hellriegel  performed  a  long 
series    of    experiments    with    different    plants,    which 

Table  V. — Barley  (Hellriegel  and  Wilfarth). 


Nitrogen  Supplied. 

Dry  Matter  Produced, 

o 

0-028 

0-056 

0-II2 
0-336 

0-5I 

3-0 

5-6 

10-8 

29-3 

showed,  up  to  a  point,  that  the  amount  of  growth  was 
very  closely  proportional  to  the  amount  of  nitrogen 
supplied  in  a  combined  form,  when  there  was  a  suffici- 
ency of  the  other  elements  of  plant  food  present. 
This  would  not  be  the  case  were  the  plant  able  to  get 
any  nitrogen  for  itself  from  the  atmosphere.  Again,  to 
meet  an  early  objection  of  Liebig  and  his  followers  that 
the  Rothamsted  crops,  which  seemed  unable  to  draw 
upon  the  nitrogen  of  the  air  though  freely  supplied 
with  phosphoric  acid  and  potash,  failed  to  do  so  because 
they  had  not  got  the  necessary  initial  development  of 
leaf,  to  one  plot  there  was  supplied  a  very  small  amount 
of  active  nitrogenous  manure,  just  to  give  the  young 
plant  a  good  start,  whereupon  it  might  be  able  to 
continue  to  feed  upon  the  atmospheric  nitrogen.  But, 
as  Table  VI.  shows,  the  small  addition  of  nitrogen  only 
produced  a  small  increase  of  crop,  very  fairly  propor- 
tional to  the  much  larger  increase  produced  by  a  normal 
application  of  the  same  fertiliser.     If,  then,  the  yield  of 


II.]        GROWTH  PROPORTIONAL  TO  NITROGEN        29 

most  of  our  field  crops  is,  until  some  other  limiting 
factor  comes  into  play,  proportional  to  the  amount  ot 
combined  nitrogen  they  receive,  it  is  necessary  to  con- 
clude that  they  have  drawn  none  from  the  atmosphere. 
It  is  indeed  true  that  the  atmosphere  does  contribute  a 
small  amount  of  nitrogen  for  the  use  of  the  plant  under 
ordinary  conditions,  because  traces  of  both   ammonia 

Table  VI.— Rothamsted  Mangolds  (1876-1902). 


Roots 

Increase 

per 

per  lb. 

Acre. 

otN. 

Tons. 

Tons. 

Superphosphate 

and  Sulphate 

of  Potash      . 

4-53 

Do. 

do. 

+   7-8  lb.  N. 

5-93 

0.17 

Do. 

do. 

+  86         „     . 

14-03 

O-II 

Do. 

do. 

+  93-8      „     • 

14-60 

0-107 

and  nitric  acid  are  found  in  the  air  and  are  washed 
out  by  the  falling  rain.  Table  VII.  shows  the  average 
amount  of  nitrogen  as  nitric  acid  and  ammonia  brought 
down  in  the  rain  falling  at  Rothamsted  for  the  thirteen 
years  between  ist  September  18S8  and  30th  August 
1901,  together  with  the  corresponding  results  obtained 
at  a  few  other  places  where  observations  have  been 
made  for  any  long  period.  It  will  be  seen  that  the 
Rothamsted  results  are  considerably  lower  than  those 
obtained  at  the  Paris,  Copenhagen,  or  Florence  stations, 
though  they  do  not  notably  dififer,  as  regards  the  total 
amount  of  nitrogen  falling  per  acre,  from  those  obtained 
at  the  two  tropical  stations  in  the  West  Indies.  The 
high  results  are  probably  due  to  the  proximity  of  towns, 
because  the  majority  of  other  determinations,  not 
quoted  here  because  they  have  only  been  continued  for 
one  or  two  years,  agree  more  nearly  with  the  Rotham- 
sted figures.     It  may  thus  be  assumed   that  ordinary 


FERTILISERS  CONTAINING  NITROGEN     [chap. 


land  receives  about  4  to  5  lb.  per  acre  per  annum  of 
combined  nitrogen  from  the  atmosphere,  an  amount 
which  only  forms  a  small  fraction  of  the  requirements 
of  the  crop  : — 

Table  VII. — Nitkogen  as  Ammonia  and  Nitric  Acid 
IN  Rain. 


Locality. 

Date. 

Rain- 
fall. 

NiTKOGKN. 

Per  MilHon. 

Pfr  Arre 
P';r  aununi. 

.2 

01  0 

<  S 

s 

< 

0   . 

s 
< 

0  . 
^1^ 

"a 
0 
H 

Rothnmsted     . 
Copenhagen     . 
Montsouris 
Florence  . 
Barbados 
British  Guiana 

18S8-1901 
1880-18S5 
1876-1900 
1869-1875 
1885-1897 
I S 90- 1 900 

27-25 
21-95 

21-^2 

3S-3I 

63-95 

102-41 

0-440 
1.97 

2-13 
1-004 
0-084 
0.055 

0-183 

0-473 

c-66 

0-57 
0.268 
0-078 

2.71 
9.27 

10-37 
8.70 

1.22 
1. 17 

I-I3 

2.21 
3-22 
3-09 

3-88 
1.82 

3-84 
11.48 

13-59 

11-79 

5.10 

2-99 

The  tenacity  with  which  in  the  face  of  such  evidence 
the  opinion  has  been  held  that  the  leaf  of  the  plant  can 
obtain  nitrogen  as  well  as  carbon  from  the  atmosphere, 
is  due  to  the  difficulty  of  explaining  how  the  world's 
original  stock  of  combined  nitrogen  can  have  arisen. 
Assuming  the  world  to  have  cooled  down  from  the 
state  of  incandescent  gas,  it  must  have  started  with  all 
its  nitrogen  in  the  free  gaseous  state  ;  yet  as  we  see  it 
to-day,  the  whole  stock  of  combined  nitrogen  is  of 
organic  origin. 

The  circulatory  process  through  which  combined 
nitrogen  passes  is  very  plain.  Animals  only  use  the 
highly  organised  compounds  like  the  proteins ;  these 
they  break  down  during  their  vital  processes  to  simpler 
compounds  like  urea  and  the  amides,  which  in  turn  are 


[I.]         ORIGIN  OF  Nil ROGEN  IN  VEGETATION         31 

taken  by  plants  and  built  up  once  more  into  the  protein 
complexes.  The  nitrogen,  however,  only  circulates 
from  one  form  of  combination  to  another,  with 
occasional  losses  when  a  compound  is  broken  down 
as  far  as  elementary  nitrogen ;  there  is  never  any 
bringing  of  fresh  elementary  nitrogen  into  the  account. 
The  stocks  of  combined  nitrogen  that  have  been  handed 
down  from  past  ages  all  speak  of  the  same  organic 
circulation,  never  of  fixation.  Coal  is  but  the  debris  of 
an  extinct  vegetation ;  nitrate  of  soda  represents  the 
glorified  result  of  the  same  decay  processes  which  give 
rise  to  nitrate  of  potash  in  India  and  nitrate  of  lime  in 
the  old  nitre  beds.  Virgin  soils  with  their  vast  stores 
of  nitrogenous  humus  are  often  looked  upon  as  having 
gained  nitrogen  by  the  accumulation  of  long  epochs  of 
vegetable  growth  ;  but  if  plants  cannot  fix  nitrogen  there 
can  have  been  no  gain,  however  long  the  growth,  but 
only  a  circulation  of  the  pre-existing  combined  stock- 
At  first  sight  there  seem  to  exist  no  processes  which  can 
either  bring  about  the  original  combination  or  renew 
the  stock  from  time  to  time.  Inorganic  agencies  are 
certainly  trifling,  because  nitrogen  is  a  difficult  element 
to  bring  into  combination,  so  great  an  initial  expenditure 
of  energy  is  required  to  separate  the  atoms  in  the 
gaseous  molecule.  Electric  sparks  will  effect  a  com- 
bination of  nitrogen  and  oxygen,  and  lightning  flashes 
through  the  air  have  been  invoked  to  account  for  the 
trace  of  nitric  acid  to  be  found  in  the  atmosphere  and 
in  rain  water.  Again,  it  has  been  supposed  that  during 
the  evaporation  of  water  there  is  always  a  slight  com- 
bination of  nitrogen  with  the  elements  of  water  to  form 
ammonium  nitrite,  but  more  recent  and  refined  experi- 
ments are  against  the  existence  of  any  such  reaction. 

There   has,  however,  of  late  years  been  discovered 
one  vital  process  capable  of  fixing  nitrogen,  which  has 


32        FERTILISERS  CONTAINING  NITROGEN     [chap. 

probably  been  operative  since  the  beginning  of  life  on 
the  earth,  and  this  power  is  the  property  of  certain 
groups  of  bacteria  only.  The  history  of  nitrogen-fixing 
bacteria  began  some  thirty  years  ago  with  the  resolu- 
tion by  Hellriegel  and  Wilfarth  of  the  great  outstanding 
difficulty  in  the  theory  that  plants  only  make  use  of 
combined  nitrogen.  Though  the  demonstration  in  the 
laboratory  of  this  opinion  seemed  perfect,  and  though 
in  the  main  it  was  corroborated  by  field  experiments, 
there  was  one  group  of  plants — peas,  beans,  clover,  and 
their  allies — which  seemed  to  derive  little  or  no  benefit 
from  nitrogenous  fertilisers,  and  yet  actually  left  the 
land  richer  in  nitrogen  after  their  growth,  although  in 
the  crop  removed  there  was  an  exceptional  amount  of 
nitrogen.  That  beans  or  vetches  or  lupins  were  the 
best  preparation  for  a  wheat  crop  was  a  commonplace 
of  Roman  agriculture,  and  the  same  observation  became 
afterwards  enshrined  in  that  most  fundamental  of 
rotations,  the  Norfolk  four-course  system,  in  which 
wheat  follows  clover  or  beans.  Hellriegel  and  Wilfarth 
found  that  leguminous  plants  did  gather  nitrogen  from 
the  atmosphere,  and  could,  therefore,  become  wholly 
independent  of  nitrogenous  manures ;  but  this  only 
took  place  when,  by  infection  from  the  soil,  certain 
characteristic  nodules  were  formed  upon  the  roots. 
These  nodules  were  found  to  be  colonies  of  a  particular 
bacterium  which  seems  to  live  symbiotically  on  the  host 
plant,  furnishing  it  with  nitrogenous  matter  and  deriving 
from  it  the  carbohydate  required  for  the  fixation  of 
nitrogen.  As  the  fixation  of  nitrogen  is  a  chemical 
process  analogous  to  going  uphill,  it  requires  a  supply 
of  energy  from  outside,  which  external  source  of  energy 
the  bacteria  obtain  by  the  oxidation  of  carbohydrate 
in  some  form  or  other.  The  particular  bacterium  living 
in   symbiosis   with    the    leguminous   plants   is    highly 


n.]  NITROGEN  FIXED  BY  LEGUMINOUS  PLANTS  33 

specialised  and  has  not  been  transferred  to  other  non- 
leguminous  plants ;  only  with  some  difficulty  has  it  also 
been  made  to  grow  and  to  fix  nitrogen  when  living 
alone  and  no  longer  in  association  with  its  host  But 
with  increasing  knowledge  of  the  methods  of  handling 
this  organism,  it  seems  probable  that  by  cultivation 
we  shall  be  able  to  obtain  races  showing  variations  in 
their  power  of  fixing  nitrogen,  though  how  long  they 
will  retain  this  greater  or  lesser  virulence  after  inocula- 
tion back  to  the  leguminous  plant  is  still  uncertain. 

The  leguminous  plants  form,  then,  by  their  associa- 
tion with  nitrogen-fixing  bacteria,  one  considerable 
natural  source  of  combined  nitrogen,  and  how  effective 
they  can  be  in  accumulating  fertilising  matter  in  the 
soil  may  be  judged  from  the  accompanying  table 
(VIII.)  showing  the  results  of  one  of  the  Rothamsted 
experiments  upon  crops  grown  in  rotation. 

Table  VIII.— Effect  of  Ci-Over  on  Succeeding  Crops. 


Manuring 

for 

Swede  Crop 

only. 

CO 

> 
0 

0 

Wheat,  1S95. 

Boots,  1896. 

Barley,  1S97. 

<3 

Isi 

£  I  > 

=  T30 

S  ° 

=■=0 

^5 

Increase 
line  to 
Clover. 

Mineral 
manure 

Complete 
manure 

Cwt-s. 

59-7 
76.7 

Lb. 
4,220 

4i547 

Lb. 
5,180 

5>209 

Per 
cent. 

+  22.7 
+  14-6 

Cwts. 
I79-I 
379-8 

Cwts. 

244-5 
388.8 

Per 

cent. 

+  36-5 
+    2.4 

Lb. 
2,103 

3.595 

Lb. 

3,991 
4.913 

Per 

cent. 

+  89-8 

+  367 

On  this  field  (Agdell)  the  rotation  begins  with  a  crop 
of  Swede  turnips,  which  is  manured,  in  one  case  with 
mineral  manures,  in  the  other  with  a  complete  fertiliser. 
Following  the  Swedes  comes  barley  without  manure, 
then  the  field  is  divided,  and  on  one  portion  clover  is 
grown,  while  the  other  is  bare  fallowed  and  carries  no 


34        FERTILISERS  CONTAINING  NITROGEN     [cHAP. 

crop  throughout  the  year.  A  crop  of  wheat,  still  un- 
manured,  completes  the  rotation.  In  the  table  the 
yield  on  the  portions  which  have  grown  clover  is  com- 
pared with  that  on  the  portions  without  crop ;  it  will 
be  seen  that  although  a  crop  of  nearly  three  tons  of 
clover  hay  has  been  taken  away  from  the  one  portion, 
the  wheat  which  follows  it  is  23  per  cent,  better  than  on 
the  portion  where  no  clover  had  been  grown  in  the 
previous  year.  Nor  is  the  benefit  due  to  the  clover 
exhausted  by  the  wheat  crop,  for  it  is  seen  to  persist  in 
the  root  crop  following  the  wheat  and  in  the  barley 
which  comes  a  year  later  still. 

The  only  practical  limitation  to  the  gathering  of 
nitrogen  by  this  method  lies  in  the  difficulty  that  is 
found  in  growing  leguminous  crops  frequently  on  the 
same  land.  Although  the  Rothamsted  experiments 
have  demonstrated  that  it  is  possible  to  grow  wheat 
year  after  year  for  more  than  half  a  century  and 
maintain  the  yield  if  the  appropriate  manures  are 
employed,  on  few  soils  can  clover  be  grown  with  success 
more  frequently  than  once  in  four  and  even  once  in 
seven  years.  As  the  farmer  says,  the  land  becomes 
"clover  sick,"  and  though  the  clover  seed  germinates 
and  grows  for  a  time,  the  constitution  of  the  plant  is  so 
weak  that  it  almost  inevitably  succumbs  during  the 
winter  to  an  attack  of  fungoid  or  other  disease.  The 
determining  cause  of  this  weakness  of  constitution 
which  lies  at  the  back  of  "clover  sickness"  is  still 
unknown,  but  preventing  as  it  does  the  more  extended 
use  of  these  nitrogen-collecting  crops  it  would  be  of 
real  economic  importance  to  find  the  cause  and  a 
remedy. 

More  recently,  however,  other  bacteria  have  been 
discovered  in  the  soil  which  are  capable  of  fixing  free 
atmospheric   nitrogen    without    association    with    any 


II.)  NITROGEN  FIXED  BY  BACTERIA  35 

host  plant,  provided  they  are  supplied  with  some  carbo- 
hydrate, by  the  oxidation  of  which  they  derive  the 
energy  necessary  to  bring  the  nitrogen  into  combination. 
Of  these  bacteria  the  best  known  and  probably  the 
most  effective  is  a  large  organism,  discovered  by 
Beijerinck  in  Holland,  and  called  by  him  Azotobacter 
chroococcum.  It  is  widely  distributed  in  cultivated  soils 
both  in  Europe  and  America,  and  although  the  author 
failed  to  detect  it  in  the  arid  soils  from  the  high  veldt 
or  the  Karoo  in  South  Africa  similar  though  perhaps 
slightly  varying  bacteria  were  obtained  from  cultivated 
soils  from  tropical  East  Africa,  Egypt,  India,  Russia, 
Western  America  and  Canada,  Sarawak,  and  Monte 
Video.  It  appears  to  be  only  active  when  there  is  some 
calcium  carbonate  in  the  soil,  possibly  because  in  its 
oxidising  reaction  certain  acids  are  produced  which  must 
be  neutralised  before  its  activity  will  continue.  Roughly 
speaking,  its  action  is  to  oxidise  carbohydrates  to 
carbon  dioxide  and  water,  forming  as  bye-products 
certain  organic  acids,  and  some  dark  brown  humus 
(whence  the  name  "chroococcum"),  and  incidentally 
bringing  a  certain  amount  of  nitrogen  into  combination, 
not  more,  however,  under  the  most  favourable  laboratory 
conditions  than  i  to  2  per  cent,  of  the  carbohydrate 
consumed.  It  is,  however,  extremely  probable  that  we 
may  look  to  this  organism  and  its  allies  as  the  origin 
of  the  continued  accumulation  of  nitrogen  in  such  rich 
virgin  soils  as  the  black  soils  of  the  Russian  Steppes  or 
of  Manitoba.  As  long  as  these  lands  were  uncultivated, 
the  annual  fall  of  the  leaf  and  dying  down  of  the  summer 
vegetation  furnished  the  conditions  necessary  for  the 
activity  of  the  Azotobacter,  The  carbohydrate-containing 
material  thus  returned  to  the  soil  provided  the  organism 
with  its  necessary  food  supply,  by  the  oxidation  of  which 
it  gained  energy  to  fix  the  atmospheric  nitrogen.     In 


36        FERTILISERS  CONTAINING  NITROGEN     [chap. 

cultivated  soils  where  the  crop  is  removed  the  action  is 
almost  brought  to  a  standstill,  as  may  be  seen  in  the 
steady  loss  of  nitrogen  from  the  arable  soils  at 
Rothamsted  during  the  fifty  years  they  have  been 
cropped  without  any  extraneous  nitrogen  supply.  Only 
when  land  is  laid  down  to  grass  is  there  a  sufficient 
amount  of  carbohydrate  debris  returned  to  the  soil  to 
enable  the  Azotobacter  to  fix  a  measurable  quantity  of 
nitrogen.  A  good  example  of  the  natural  accumulation 
of  combined  nitrogen  may  be  seen  in  two  pieces  of 
land  at  Rothamsted,  which  for  the  last  twenty-five 
years  have  been  allowed  to  run  wild  and  assume  a 
natural  prairie  condition  of  self-sown  weeds  and  grasses, 
that  are  never  taken  away  but  left  to  rot  where  they  die 
down.  Samples  of  the  soil  had  been  taken  at  the 
beginning  of  the  period,  and  by  comparing  them  with 
more  recently  taken  samples  it  has  been  possible  to 
detect  a  very  considerable  fixation  of  nitrogen, 
amounting  in  the  most  favourable  case  to  nearly  fifty 
pounds  of  nitrogen  per  acre  per  annum.  The  second 
similar  piece  of  land  shows  a  much  lower  result,  and  this 
is  correlated  with  the  lack  of  carbonate  of  lime  in  the 
soil  of  this  plot  and  a  corresponding  absence  of  the 
Azotobacter  organism. 

It  is  too  early  yet  to  speculate  freely  on  the 
work  of  the  various  nitrogen-fixing  bacteria ;  we  may, 
however,  confidently  attribute  to  their  action  both  the 
current  stock  of  combined  nitrogen  in  the  world  and 
the  main  source  of  its  renewal  in  the  future. 

Attempts  have  already  been  made  to  raise  the 
nitrogen-fixing  bacteria  artificially,  particularly  those 
associated  with  leguminous  plants,  and  by  introducing 
them  into  soil  that  is  lacking  or  poorly  supplied  with 
them,  to  render  it  capable  of  self-enrichment  in  this 
most  natural  manner.     Such  cultures  are,  in  fact,  sold 


II.]  SOIL  INOCULATION  37 

* 

commercially  at  the  present  time  and  have  in  some 
cases  been  somewhat  unscrupulously  boomed  as 
dispensing  with  the  need  for  nitrogenous  fertilisers. 
Undoubtedly  cases  may  be  quoted  where  the  use  of 
these  pure  cultures  of  nodule-forming  bacteria  has 
been  of  great  service,  generally  on  newly-reclaimed 
soils,  which  have  thus  become  for  the  first  time  capable 
of  carrying  a  leguminous  crop.  But  in  old  cultivated 
soils  the  organism  is  already  present,  and  sufficient 
evidence  is  not  yet  forthcoming  to  show  that  the  new 
introductions  have  had  any  effect ;  certainly  the  results 
obtained  in  the  British  Isles  are  almost  wholly  negative. 
Doubtless  the  useful  soil  bacteria  will  be  domesticated, 
improved,  and  made  more  effective,  just  as  our  flocks 
and  herds  have  been  tamed  and  developed,  while  the 
useless  ones  will  be  stamped  out  as  vermin  ;  but  at  the 
present  time  we  cannot  be  satisfied  that  any  improved 
race  of  bacteria  introduced  artificially  into  the  soil  has 
managed  to  persist  and  get  a  real  footing  in  face  of  the 
competition  of  the  enormous  natural  bacterial  flora 
already  existing  there.  So  the  picture  of  the  farmer 
carrying  the  manure  for  a  field  in  his  waistcoat  pocket  and 
applying  it  with  a  hypodermic  syringe,  is  still  a  vision 
of  the  future. 

These  natural  processes  for  the  recuperation  of  our 
stock  of  combined  nitrogen  have,  during  the  last  year 
or  two,  been  supplemented  by  one  or  two  manufacturing 
processes  of  great  interest  in  themselves,  which  are  on 
the  point  of  becoming  factors  of  importance  in  the 
fertiliser  market. 

Speaking  broadly,  there  are  two  ways  of  bringing 
free  nitrogen  gas  into  combination  :  first,  at  extremely 
high  temperatures,  such  as  are  attained  in  the  electric 
arc  or  sparks,  nitrogen  will  combine  with  oxygen  to 
form  various  oxides  from  which  nitric  acid  will  eventually 


38        FERTILISERS  CONTAINING  NITROGEN     [chap. 

result  by  solution  in  water;  secondly,  nitrogen  will 
combine  with  a  few  metals  and  allied  bodies,  again  at 
high  temperatures,  to  yield  substances  which  under  the 
action  of  water  give  rise  to  ammonia.  It  is  this  latter 
method  which  was  first  developed  on  a  commercial 
scale  by  Frank  and  Caro  in  Berlin.  They  did  not 
exactly  start  with  a  metal,  but  with  calcium  carbide, 
the  substance  now  so  well  known  as  the  source  of 
acetylene  for  illumination.  This  body,  Frank  and 
Caro  found,  would  combine  readily  with  nitrogen  gas 
at  quite  moderate  temperatures,  and  the  resulting  sub- 
stance, calcium  cyanamide,  nitrolim,  or  kalk-stickstoff, 
as  it  is  called,  will  decompose  under  the  action  of  water, 
yielding  its  nitrogen  as  ammonia  and  the  calcium  and 
carbon  as  calcium  carbonate.  An  Italian  company, 
which  was  the  first  to  take  up  the  patents  for  the 
manufacture  of  calcium  cyanamide,  has  established  its 
factory  alongside  one  of  the  great  producers  of  calcium 
carbide  at  Piano  d'Orte  in  the  hills  above  Rome,  where 
water-power  can  be  obtained  for  the  cheap  generation 
of  electricity,  and  other  works  are  being  erected  in 
Norway,  in  Savoy,  and  in  America,  where  suitable 
water-power  can  be  obtained.  On  theoretical  grounds, 
one  electrical  horse-power  per  annum  should  bring 
about  the  fixation  of  772  kilogrammes  of  nitrogen ;  in 
practice  300  to  330  have  been  attained.  In  the  manu- 
facturing process  the  calcium  carbide  is  first  roughly 
ground  and  then  heated  in  iron  tubes  through  which  a 
current  of  nitrogen  gas  is  passed.  The  calcium  carbide, 
which  itself  results  from  the  reaction  of  a  mixture  of 
chalk  and  coke  in  the  electric  furnace,  must  either  be 
purchased  or  manufactured  by  a  preliminary  process. 
The  two  reactions  of  forming  the  carbide  and  uniting 
it  with  nitrogen  can  indeed  be  carried  out  simultaneously, 
but  this  method  has  been  abandoned  in  practice.     The 


11.]  CHEMICAL  FIXATION  OF  NITROGEN  39 

nitrogen  gas  is  obtained  by  passing  a  current  of  air 
over  red-hot  copper,  the  copper  oxide  formed  being 
afterwards  reduced  to  the  metallic  state  again  by  sending 
over  it  a  current  of  coal-gas  while  it  is  still  hot.  More 
recently  a  process  of  obtaining  nitrogen  by  fractional 
distillation  from  liquefied  air  has  been  employed.  The 
resulting  calcium  cyanamide  is  a  very  fine  dark  grey 
powder,  light  and  rather  difficult  to  sow  alone  because 
it  floats  so  readily  in  the  air. 

Since  the  product  also  contains  about  20  per  cent. 
of  free  lime,  it  readily  absorbs  water  from  the  atmo- 
sphere, the  first  change  that  takes  place  being  the 
slaking  of  the  quicklime.  At  the  same  time  the  cyan- 
amide  begins  to  decompose  slowly  into  ammonia  and 
calcium  carbonate  in  eventual  accordance  with  the 
equation 

CaCN2  +  3H20  =  2NH3  4-CaC03, 

so  that  some  loss  of  ammonia  may  take  place  if  the 
manure  is  left  lying  about  exposed  in  a  loose  condi- 
tion to  the  atmosphere.  In  bags,  however,  it  may  be 
stored  without  any  sensible  loss. 

With  superheated  steam  the  reaction  takes  place 
more  rapidly,  and  with  acids  or  acid  manures  salts  of  cal- 
cium and  ammonium  are  formed,  preceded  of  course  by 
an  active  interaction  between  the  free  lime  and  the 
acid.  The  same  reaction  may  be  expected  to  take 
place  when  calcium  cyanamide  is  applied  to  the  soil : 
it  should  change  slowly  into  ammonia,  which  will  be 
arrested  by  the  soil,  and  calcium  carbonate.  It  has 
been  shown,  however,  by  Lohnis,  that  the  reaction  with 
water  alone  is  slow  and  not  particularly  effective,  but 
that  in  practice  certain  soil  bacteria  bring  about  the 
change. 

Commercial   cyanamide   contains    as    much    as    20 


40       FERTILISERS  CONTAINING  NITROGEN     [chap. 

per  cent,  of  nitrogen,  the  theoretical  substance  being 
CaCNg  with  35  per  cent,  of  nitrogen.  As  a  fertiliser, 
calcium  cyanamide  has  been  subjected  to  a  series 
of  sufficiently  conclusive  trials  which  show  that  on  most 
soils  it  is  almost  but  not  quite  as  effective  as  sul- 
phate of  ammonia  supplying  an  equal  amount  of 
nitrogen.  For  example,  Table  IX.  shows  the  results  of 
four  trials  at  Rothamsted  in  1905,  mangolds  and 
barley  being  the  crops  under  experiment.  On  soils 
poor    in    lime,  doubtless    the    cyanamide   would  give 

Table  IX. — Rothamsted  Experiments  with  Calcium  Cyanamide, 

1905. 


Barley. 

Mangolds. 

Grain. 

Straw. 

Calcium  Cyanamide 
Sulphate  of  Ammonia  . 

Bushels. 
34-3 
37-5 

Cwts. 

19 

24 

Tons. 
22-0 

23-5 

Tons. 
II-I 
lO-O 

Tons. 
28-9 
27-9 

comparatively  better  results,  because  then  the  carbonate 
of  lime,  which  is  the  bye-product  of  the  decomposition 
taking  place  in  the  soil,  would  itself  be  of  considerable 
value.  The  Rothamsted  soil,  however,  contains  sufifiicient 
carbonate  of  lime  to  minimise  the  effect  of  this  factor. 
The  chief  drawback  to  the  practical  employment  of 
calcium  cyanamide  as  a  manure  is  its  light,  blow-away 
character,  and  the  injurious  effect  upon  germinating  seeds 
of  the  ammonia  and  other  gases  given  off  when  it  is 
first  applied  to  the  soil.  It  has,  therefore,  to  be  sown 
on  the  land  alone,  and  it  should  be  incorporated  with 
the  soil  a  week  or  so  before  any  seed  is  sown.  For 
similar  reasons  it  should  not  be  used  as  a  top  dressing 
unless  mixed  with  earth  beforehand,  though  recent 
experiments    suggest    that    this    objection    has    been 


II.]  CALCIUM  CYAN  AM  IDE  41 

exaggerated.  It  is  best  to  mix  the  cy anamide  witli 
superphosphate  before  application  to  the  land  ;  in  most 
cases  when  cyanamide  is  used  phosphates  will  also  be 
required,  and  a  mixture  of  cyanamide  with  from  five  to 
ten  times  its  weight  of  superphosphate  can  be  con- 
veniently made  and  forms  a  good  fertiliser  for  barley 
or  turnips.  The  mixture  should  be  made  on  the 
floor  of  the  manure  shed  at  least  a  day  before  the 
manure  has  to  be  sown ;  if  the  cyanamide  is  care- 
fully handled  and  covered  with  superphosphate,  it 
can  be  mixed  without  creating  an  unbearable  dust. 
With  the  slaking  of  the  lime  a  good  deal  of  heat  is 
developed  and  the  manure  begins  to  steam,  but  a 
sprinkling  from  a  watering  pot  will  help  to  keep  the 
heat  down  without  rendering  the  mixture  in  any  way 
difficult  to  handle.  The  heap  should  be  turned  over 
two  or  three  times  to  secure  a  good  mixture,  and  left 
until  the  next  day  to  cool  off.  It  remains  in  a  nice 
friable  condition  and  undergoes  practically  no  further 
change  if  it  cannot  be  sown  at  once.  No  unpleasant 
gases  are  given  off  during  the  mixing;  the  samples 
of  cyanamide  first  made  contained  some  unchanged 
calcium  carbide  which  gave  off  acetylene  on  wetting, 
but  this  is  now  avoided  in  the  manufacturing  process. 

Two  methods  have  been  adopted  to  obviate  the 
dustiness ;  in  one  the  product  is  treated  with  a  small 
proportion  of  heavy  shale  or  coal  oil,  in  the  other  just 
sufficient  treatment  with  steam  is  applied  to  convert 
the  quicklime  into  slaked  lime,  and  give  the  material 
a  more  granular  form.  This  latter  process  has  the 
further  advantage  of  decomposing  any  traces  of  calcium 
carbide  and  phosphide  that  may  be  present  in  the 
original  material.  A  slightly  different  product  con- 
taining calcium  cyanamide  is  manufactured  by  a  firm 
in  Westeregeln,  under  the  patents  of  F.   Polzenius,  by 


42        FERTILISERS  CONTAINING  NITROGEN     [chap. 

heating  a  mixture  of  calcium  carbide  and  chloride  in  a 
stream  of  pure  nitrogen  at  about  750°  C.  The  product, 
known  as  stickstoff-kalk,  is  a  black  powder  containing 
over  20  per  cent,  of  nitrogen  and  about  10  per  cent,  of 
calcium  chloride,  together  with  a  considerable  amount 
of  free  lime.  As  a  manure  stickstoff-kalk  behaves  in  all 
essential  respects  like  the  kalk-stickstoff  oi  v^YiXoh  a  more 
detailed  description  has  been  given. 

The  other  method  of  bringing  nitrogen  into  com- 
bination— that  of  effecting  its  union  with  oxygen  at 
the  temperature  of  the  electric  arc — has  received  con- 
siderable attention,  and  forms  the  base  of  at  least  two 
working  processes.  It  will  be  remembered  that  when 
Sir  William  Crookes  in  1898,  in  his  British  Association 
address,  warned  the  world  of  the  rapidly  progressive 
exhaustion  of  its  supplies  of  combined  nitrogen,  it  was 
to  the  union  of  nitrogen  with  oxygen  that  he  looked 
for  the  future  supply  of  combined  nitrogen  for  the 
wheat  crop,  and  he  showed  experimentally  how  the 
two  gases  would  burn  together  at  a  very  high  tempera- 
ture. Not  enough  heat,  however,  is  given  out  by  the 
flame  to  bring  more  gas  up  to  the  ignition  point,  hence 
the  flame  is  only  continuous  as  long  as  external  energy 
is  poured  in. 

Calculating  from  the  best  results  Lord  Rayleigh 
had  obtained  in  bringing  nitrogen  and  oxygen  into 
combination  by  the  electric  spark,  Crookes  decided  that 
if  electricity  could  be  generated  at  one-seventeenth  of 
a  penny  per  Board  of  Trade  unit,  as  it  was  expected 
would  be  the  case  at  Niagara,  then  nitrate  of  soda 
could  be  made  artificially  at  about  £^  per  ton. 

Such  an  electrical  process  was  installed  at  Niagara 
by  Bradley  and  Lovejoy,  who  produced  a  number  of 
arcs  between  platinum  poles  with  a  continuous  current 
zX  a  potential  of  10,000  volts.     The  oxides  of  nitrogen 


II.]  ELECTRICAL  FIXATION  OF  NITROGEN         43 

generated  were  converted  into  nitric  and  nitrous  acids 
by  steam  and  more  oxygen,  and  a  mixture  of  sodium 
nitrite  and  nitrate  was  prepared  for  agricultural  pur- 
poses. The  installation,  however,  only  ran  for  fifteen 
months,  for  though  considerable  amounts  of  nitric 
acid  were  produced,  technical  difficulties  in  maintaining 
the  apparatus  in  working  order  proved  insuperable. 
More  recently  a  working  process  has  been  devised  by 
Berkeland  and  is  running  on  a  commercial  scale  at 
Notodden  in  Norway.  In  the  Berkeland-Eyde  process 
an  alternating  current  at  about  5000  volts  is  set  to  form 
an  arc  between  U-shaped  copper  electrodes,  which  are 
hollow  and  kept  cool  by  a  current  of  water  within. 
The  electrodes  are  placed  equatorially  between  the 
poles  of  a  powerful  electro-magnet,  which  has  the 
effect  of  causing  the  arc  to  spread  out  into  a  broad 
flat  flame.  Though  the  temperature  of  the  arc-flame 
is  calculated  to  be  2600°  C,  it  is  not  particularly 
luminous;  it  may  be  looked  at  directly  from  a  yard's 
distance. 

Through  the  furnace  in  which  this  special  arc  is 
generated  about  15,000  litres  of  air  are  blown  per 
minute  at  gentle  pressure  and  the  issuing  air  contains 
about  I  per  cent,  of  nitric  oxide  and  is  at  a  temperature 
of  600°  to  700°  C.  It  is  cooled  and  then  passes  into 
two  oxidising  chambers,  where  the  combination  of  the 
nitric  oxide  with  the  oxygen  of  the  uncombined  air 
takes  place,  after  which  it  passes  into  a  series  of  five 
condensing  towers.  Down  the  fourth  tower,  which 
is  filled  with  broken  quartz,  water  trickles  and  picks 
up  enough  of  the  nitrous  gases  to  become  5  per 
cent,  nitric  acid  at  the  bottom ;  this  is  pumped  up 
and  trickles  down  the  third  tower,  the  process  being 
repeated  until  the  liquid  leaving  the  bottom  of  the 
first  tower  contains  50  per  cent,  of  nitric  acid.     In  the 


44        FERTILISERS  CONTAINING  NITROGEN     [chap. 

fifth  and  last  tower  the  absorbing  liquid  is  milk  of  lime, 
and  the  resulting  mixture  of  solution  of  calcium  nitrite 
and  nitrate  is  treated  with  enough  of  the  previously- 
formed  nitric  acid  to  convert  it  wholly  into  nitrate, 
the  nitrous  fumes  evolved  being  led  back  into  the  oxi- 
dising chambers.  The  product  is  then  concentrated 
until  it  solidifies  as  a  material  containing  about  13 
per  cent,  of  nitrogen,  or  75  per  cent,  of  pure  calcium 
nitrate. 

The  present  factory  has  three  electric  furnaces 
installed,  each  employing  500  kilowatts,  and  the  pro- 
duction amounts  to  about  150  kilogrammes  of  nitrogen 
fixed  per  kilowatt  year. 

Berkeland  calculates  that  the  cost  of  manufacturing 
calcium  nitrate  containing  13  per  cent,  of  nitrogen 
is  about  £/\.  per  ton,  and  that  it  can  be  sold  at  a 
profit  at  ;;^8  a  ton,  which  would  be  equivalent  to  nitrate 
of  soda  at  about  ;^io  a  ton.  The  present  large  factory 
at  Notodden  has  been  putting  calcium  nitrate  on  the 
market  for  two  years  or  more,  the  rate  of  pro- 
duction now  being  about  20,000  tons  per  annum. 
When  the  extensions  to  the  factory  are  completed  it 
is  expected  the  output  will  amount  to  nearly  3000  tons 
per  month.  As  a  fertiliser  there  cannot  be  the  least 
doubt  that  nitrate  of  lime  will  be  just  as  valuable, 
nitrogen  for  nitrogen,  as  nitrate  of  soda.  At  Rotham- 
sted  a  chemically  prepared  nitrate  of  lime  has  been 
used  for  two  or  three  years  for  a  special  purpose  on  one 
of  the  mangold  plots,  and  it  has  given  exactly  equal 
results  to  the  nitrate  of  soda  plot  alongside.  Many 
field  experiments  have  also  been  carried  out  with  the 
electrical  product  in  Norway  during  the  last  year  or 
two,  and  have  shown  that  the  new  material  can  be 
strictly  valued  against  nitrate  of  soda  on  the  basis  of 
the    nitrogen   it  contains.     Indeed,  on    some    soils    it 


11.]  NITRATE  OF  SODA  45 

is  likely  to  be  more  valuable,  because,  as  will  be 
shown  later,  part  at  least  of  the  lime  base  will  be 
left  behind  in  the  soil  as  calcium  carbonate.  This 
will  be  an  advantage  in  peaty  soils,  and  will  also  save 
clay  soils  from  the  peculiar  wetness  and  stickiness 
which  results  from  the  employment  of  much  nitrate 
of  soda.  The  present  price  is  about  ^8,  8s.  per  ton  at 
the  British  ports. 

Turning  now  from  the  atmospheric  nitrogen  and 
the  various  possibilities  of  utilising  it  to  the  purely 
nitrogenous  fertilisers  that  are  available,  we  can  begin 
by  dividing  them  into  two  classes,  the  quick  and  the 
slow  acting,  in  the  first  of  which  we  have  practically  only 
nitrate  of  soda,  sulphate  of  ammonia,  cyanamide,  and 
nitrate  of  lime.  Our  acquaintance  however  with  the  two 
latter  is  too  limited  as  yet  to  enable  us  to  do  more  than 
predict  that  they  will  fall  into  line  with  sulphate  of 
ammonia  and  nitrate  of  soda  respectively.  Nitrate  of 
soda  has  now  been  in  use  in  this  country  for  something 
like  seventy  years,  the  Chilian  deposits  having  been 
first  discovered  about  the  time  of  Darwin's  voyage 
round  the  world  in  the  Beagle.  As  nitre  had  long 
been  known  to  possess  great  manurial  value,  the 
exportation  of  nitrate  of  soda  to  Europe  was  at  once 
suggested,  and  in  1830  it  appears  that  a  trial  ship- 
ment was  made  of  18,700  quintals  of  about  100  lb. 
each.  By  1838,  the  date  of  the  first  volume  of  the 
Journal  of  the  Royal  Agricultural  Society^  it  was  being 
tried  experimentally  by  a  good  many  landlords  and 
farmers  in  this  country.  The  production  grew  rapidly, 
and  reached  its  maximum  in  1899,  when  1,344,550  tons 
were  consumed  ;  since  then  the  output  has  declined  a 
little,  owing  to  combination  between  the  producers. 
At  the  present  time  the  United  Kingdom  takes  about 
one-twelfth  of  the  total  production,  Belgium  an  equal 


46        FERTILISERS  CONTAINING  NITROGEN     [chap. 

share,  France  and  the  United  States  about  one-sixth 
each,  and  Germany  rather  more  than  one-third  of  the 
whole.  Opinions  differ  greatly  as  to  the  approaching 
exhaustion  of  the  Chilian  deposits ;  various  estimates 
set  their  probable  life  at  from  twenty  to  forty  years, 
but  doubtless  long  before  exhaustion  sets  in  the 
poorer  grounds,  now  being  neglected  as  containing 
less  than  the  paying  amount  of  nitrate,  will  be  exploited, 
provided  always  that  the  artificial  nitrate  of  lime  does 
not  render  the  whole  industry  unprofitable. 

As  to  the  origin  of  the  nitrate  of  soda  deposits  there 
are  two  theories,  to  understand  which  some  description 
of  the  mode  of  occurrence  is  necessary.  The  chief 
deposit  lies  in  the  province  of  Tarapaca,  in  Chile,  on 
an  elevated  plain,  about  3000  feet  above  sea  level,  known 
as  the  Pampa  of  Tamarugal,  which  stretches  for  a  breadth 
of  some  thirty  or  forty  miles  from  the  Corderillas  on 
the  eastward  to  a  low  range  of  foothills  separating  it 
from  the  sea.  The  climate  is  intensely  dry,  rain  falling 
only  every  two  or  three  years,  and  then  in  quantities  so 
small  as  to  evaporate  rapidly.  The  special  nitrate-bearing 
deposit  or  caliche  occurs  a  few  feet  below  the  surface, 
and  in  it  the  nitrate  is  associated  with  earthy  matters, 
gypsum,  common  salt,  and  sulphates  of  sodium  and 
potassium.  The  generally  accepted  theory  regards  the 
plain  as  an  ancient  sea-bed  elevated  by  one  of  the 
volcanic  movements  common  on  that  coast,  and  then 
desiccated.  The  nitrate  of  soda  is  set  down  to  the 
oxidation  of  immense  masses  of  seaweed  present  in  the 
original  sea,  the  salt  of  which  has  provided  the  necessary 
sodium  base.  The  chief  argument  in  support  of  this 
supposition  is  the  presence  of  a  small  amount  of  sodium 
iodate  in  the  crude  caliche,  seaweed  being  known  to 
contain  iodine.  But  such  a  theory  is  as  impossible  on 
chemical   grounds   as   it  is   untenable  geologically.     It 


11.]  FORMATION  OF  NITRATE  OF  SODA  4? 

involves,  in  the  first  place,  an  extravagant  amount  of 
seaweed,  and  our  knowledge  of  the  nitrification  process 
is  quite  opposed  to  the  idea  that  it  would  take  place  in 
a  rapidly  concentrating  medium  containing  common 
salt.  Nor  have  we  any  reason  to  suppose  that  salt 
would  supply  a  base  for  nitrification  ;  even  if  its  hydro- 
chloric acid  could  be  turned  out  the  liberated  acid 
would  at  once  suspend  the  process.  And  again,  if  the 
iodates  are  to  be  taken  as  indicating  seaweed,  why 
are  not  bromates  also  present  in  the  caliche,  since 
both  bromine  and  iodine  are  associated  in  seaweed. 

A  much  more  probable  theory  is  that  the  deposit 
represents  the  saline  residues  of  fresh-water  streams 
flowing  off  the  Corderillas,  containing  nitrates  and 
other  salts  derived  from  old  rich  soils  or  rocks  on  the 
heights.  The  evaporation  of  such  waters  for  a  long 
period  of  progressive  desiccation  would  result  in  the 
accumulation  of  the  dissolved  salts  in  the  dry  region 
over  which  the  waters  formerly  spread  when  the  rainfall 
was  greater.  The  occurrence  of  iodine  cannot  be 
explained  until  more  is  known  as  to  the  amount  of 
this  element  present  in  the  waters  and  soils  of  the 
Corderillas. 

The  only  other  deposits  of  nitrate  of  soda  v\^hich 
assume  any  economic  importance  are  those  which 
occur  in  Upper  Egypt,  where  certain  shale  beds  of 
Eocene  age,  out-cropping  on  both  sides  of  the  Nile 
between  Qena  and  Assouan,  contain  enough  sodium 
nitrate  to  make  the  clay  worth  carriage  as  a  manure 
known  locally  as  "  tafia."  Analyses  of  a  series  of  these 
shales  by  F.  Hughes  show  an  average  of  ^-y  per 
cent,  of  nitrate  of  soda  associated  with  lo-i  per  cent,  of 
sodium  chloride,  and  5-4  per  cent,  of  sodium  sulphate. 
The  material  is  disseminated  throughout  the  whole 
bulk  of  the  clay ;  and  as  this  is  not  permeabk  to  any 


48        FERTILISERS  CONTAINING  NITROGEN     [cHAP. 

extent  by  water,  the  nitrate  can  hardly  be  due  to 
infiltration,  but  must  have  been  formed  in  situ  —  a 
conclusion  which  is  much  strengthened  by  the  fact 
brought  out  by  Hughes'  analysis  that  small  quantities 
of  nitrogenous  organic  matter,  ammonia  and  nitrites 
are  also  present  in  the  extract  from  the  clay. 

In  all  probability  the  nitrates  in  these  shales  repre- 
sent the  results  of  nitrification  of  a  mass  of  organic 
matter  originally  contained  in  the  deposit,  but  until 
further  data  have  been  accumulated  as  to  the  depth  to 
which  the  nitrates  extend,  and  their  replacement  or 
not  by  unoxidised  organic  nitrogen  compounds  at 
depths  beyond  the  access  of  atmospheric  oxygen,  it  is 
impossible  to  say  whether  we  are  dealing  with  recent 
or  with  what  might  be  termed  fossil  nitrification,  or 
again  whether  there  has  been  any  concentration  of  the 
salts  in  the  surface  layer  analysed. 

In  any  case,  these  Egyptian  deposits  give  a  clue  to 
the  possible  origin  of  the  Chile  beds  by  washing  from 
similar  strata  (and  the  Corderillas  consist  of  rocks  of 
recent  age)  into  a  rainless  area,  where  the  salts  are 
accumulated  by  evaporation.  The  two  deposits  present 
this  common  difficulty  :  that  the  deposit  is  nitrate  of  soda 
instead  of  nitrate  of  lime — the  usual  product  of  nitrification 
in  soil ;  again,  both  are  associated  with  a  preponderance 
of  sulphates  over  chlorides,  a  fact  which  seems  to  put 
any  marine  origin  out  of  the  question.  We  are,  how- 
ever, dealing  with  typically  arid  conditions,  and  in  all 
parts  of  the  world  sodium  salts  are  characteristically 
abundant  in  the  soils  and  rocks  of  areas  of  small  rainfall ; 
indeed,  sodium  carbonate  is  always  found  in  such  cases, 
and  this  would  form  the  base  for  nitrification.  At  the 
same  time,  similar  oxidising  processes  to  those  which 
give  rise  to  nitrates  would  convert  the  sulphur  of  the 
organic  matter  to  sulphates.     But  to  settle  the  problem 


II. J  PREPARATION  OF  NITRATE  OF  SODA  49 

of  the  origin  of  the  Chile  deposits  of  nitrate  of  soda,  an 
examination  is  required  of  the  salts  in  the  rocks  of  the 
Corderillas,  the  drainage  from  which  would  find  its  way 
into  the  plain  of  Tamarugal. 

The  nitrate  of  soda  is  found  in  a  deposit  named 
caliche,  of  which  it  constitutes  from  60  per  cent,  down  to 
17  per  cent,  lower  grades  not  being  at  present  worked. 
In  the  caliche  it  is  associated  with  sodium  chloride, 
sulphates  of  calcium,  sodium,  and  potassium,  and  a 
varying  proportion  of  insoluble  earthy  matter.  The 
caliche  is  not  found  on  the  surface,  but  is  covered  by 
various  earthy  and  gypseous  deposits  to  the  depth  of  2 
to  10  feet.  After  the  deposit  has  been  broken  up  by 
blasting,  the  caliche  is  removed  to  the  works,  broken  up 
and  lixiviated  in  large  vats  heated  by  steam.  The 
saturated  solution  is  led  into  tanks  in  which  the  nitrate 
of  soda  deposits  on  cooling,  further  crops  being 
obtained  from  the  mother  liquors  by  continuing  the 
treatment.  After  draining  and  drying  the  nitrate  is 
made  up  into  2-cwt.  bags  for  export.  A  further 
product  of  the  nitrate  process  is  iodine,  because  the 
caliche  always  contains  a  small  quantity  of  sodium 
iodate.  The  nitrate  of  soda  thus  obtained  is  a  coarsely 
crystalline  powder,  varying  in  colour  from  a  slight 
brown  or  pink  shade  to  a  grey-white,  containing  95  to 
96  per  cent,  of  pure  sodium  nitrate,  the  remainder  being 
made  up  of  moisture,  sodium  chloride,  and  traces  of 
sulphates  of  sodium,  magnesium,  and  calcium. 

A  sample  of  the  crystals  after  drying  in  the  sun  had 
the  following  composition  : — 


Sodium  Nitrate    . 

94-164 

Magnesium  Chloride 

0-289 

Potassium  Nitrate 

.       1763 

Calcium  Sulphate 

0-102 

Sodium  Chloride  . 

0-933 

Insoluble  matter  . 

0-138 

Sodium  Iodate 

O-OIO 

Water  . 

2-IOO 

Potassium  Perchlorate 

0-282 

lOO-OO 

Magnesium  Sulphate 

0-219 

D 


50        FERTILISERS  CONTAINING  NITROGEN     [chap. 

The  salt  is  very  soluble  in  water  and  is  deliquescent, 
so  that  it  will  gradually  absorb  enough  water  to  liquefy 
when  exposed  to  the  damp  air  of  an  English  winter  in 
a  manure  shed.  The  salt  is  poisonous  in  quantity,  awd 
both  horses  and  stock  have  not  infrequently  been  killed 
by  licking  nitrate  of  soda  or  the  bags  in  which  it  has 
been  stored.  Nitrate  of  soda  contains  as  much  as  56 
per  cent,  of  oxygen  and  accelerates  the  combustion  of 
such  bodies  as  wood  or  coal  with  almost  explosive 
violence,  one  accident  at  least  has  been  recorded  from 
this  source  of  danger.  Nitrate  of  soda  is  not  only 
soluble  in  water,  but  it  is  not  in  any  way  retained  by 
the  soil,  so  that  it  must  wash  through  into  the  drains  or 
subsoil  when  percolation  is  going  on.  For  this  reason 
it  should  only  be  applied  as  a  top  dressing  when  the 
crop  is  growing.  Like  all  other  saline  bodies  which 
form  a  strong  solution  with  water,  nitrate  of  soda  will 
scorch  and  destroy  any  green  tissue  with  which  it  is  left 
in  contact ;  it  withdraws  water  from  the  cells  and  kills 
them  by  plasmolysis  (see  p.  18).  Hence  in  sowing 
nitrate  of  soda  on  a  crop  like  cabbage,  a  certain  amount 
of  care  should  be  taken  not  to  let  the  salt  lodge  in 
the  crown  of  the  plant. 

Nitrate  of  soda  may  be  mixed  with  other  manures 
except  superphosphates  and  dissolved  bones,  the  acid  of 
which  gradually  liberates  nitric  acid,  so  that  such  a 
mixture  should  be  sown  immediately  after  it  has  been 
made. 

Nitrate  of  soda  is  always  sold  by  the  producers  with 
a  guarantee  of  95  per  cent,  pure,  which  guarantee 
should  also  be  obtained  by  the  farmer,  for  the  material 
should  be  sold  exactly  as  it  is  imported.  It  usually 
contains  about  96  per  cent,  of  pure  sodium  nitrate, 
which  is  equivalent  to  15-7  per  cent,  of  nitrogen  or  19-1 
per  cent,  of  ammonia. 


II.]  IMPURITIES  IN  NITRATE  OF  SODA  51 

Sodium  perchlorate  is  sometimes  present  in  small 
quantities  as  an  impurity ;  this  has  a  very  injurious 
effect  upon  vegetation,  but  the  instances  of  damage  due 
to  this  cause  are  uncommon.  Adulteration  of  nitrate  of 
soda  has  become  rare  nowadays ;  in  the  past  (and  to  a 
certain  extent  still)  it  was  mixed  with  common  salt,  a 
substance  which  it  resembles  in  colour  and  crystalline 
appearance.  In  the  manufacture  of  gunpowder  it  is 
customary  to  make  potassium  nitrate  by  mixing  sodium 
nitrate  with  potassium  chloride  and  crystallising  out  the 
less  soluble  nitre.  The  mother  liquors  contain  sodium 
chloride  (common  salt)  with  small  quantities  of  the 
more  valuable  potassium  nitrate,  and  when  evaporated 
down  yield  what  is  sometimes  known  as  "  gunpowder 
salt."  On  occasion  this  material  has  been  sold  at  a 
fraudulent  price  as  "  nitrate  of  salt,"  and  credited  with 
being  a  combination  of  nitrate  of  soda  and  salt,  more 
valuable  than  either  for  such  crops  as  mangolds. 

As  there  is  no  occasion  for  any  admixture  with 
nitrate  of  soda,  the  farmer  should  always  insist  on 
buying  the  unmixed  substance  of  standard  purity. 

As  a  manure,  nitrate  of  soda  is  of  course  treated  as 
a  source  of  nitrogen.  It  is  not  sufficiently  realised  how 
valuable  the  soda  base  may  be.  This  is  not  because 
soda  is  in  any  way  necessary  to  the  nutrition  of  the  plant, 
but  because  of  the  action  of  any  soluble  salt  upon  the 
insoluble  potash  compounds  in  the  soil.  The  potash  of 
the  soil  is  due  to  the  partial  weathering  of  double 
silicates  like  felspar  into  clay,  which  is  not  to  be 
regarded  as  pure  kaolinite,  AlgOg  2Si02  sHgO,  but  as 
containing  a  certain  proportion  of  zeolitic  bodies  inter- 
mediate between  felspar  and  kaolinite — hydrated  double 
silicates  containing  potash,  soda,  magnesia,  and  lime 
combined  with  alumina  and  silica.  Any  soluble  salt, 
and   particularly  a   soluble    soda   salt,  will    react    with 


52        FERTILISERS  CONTAINING  NITROGEN     [chap. 

these  zeolites  and  exchange  bases  to  an  extent  depend- 
ing upon  the  relative  masses  of  the  two  bodies ;  hence 
nitrate  of  soda  acts  on  the  clay  in  the  soil  and  brings  a 
little  potash  into  solution.  To  such  an  extent  does  this 
action  take  place  that  in  practice  a  dressing  of  nitrate 
of  soda  on  any  but  the  lightest  soils  will  dispense  with 
the  necessity  of  a  specific  potash  manuring,  even  for 
potash-loving  crops. 

This  is  well  illustrated  in  the  Rothamsted  experi- 
ments (see  Table  X.)  upon  mangolds,  if  we  compare  the 
yields  on  the  plots  receiving  equivalent  amounts  of 
nitrogen  as  nitrate  of  soda,  sulphate  of  ammonia,  and 
rape  cake,  both  with  and  without  potash.  The  table 
refers  to  the  season  of  1900,  the  twenty-fifth  year  of 
that  series  of  experiments,  when  it  might  be  sup- 
posed the  potash  in  the  soils  of  the  plots  receiving  no 
potash  in  the  manure  must  have  become  thoroughly 
exhausted : — 


Table  X.— Effect  of  Soda  in  Nitrate  of  Soda,  Mangolds, 
Rothamsted,  1900. 


Plot. 

With 
Nitrate 

of 
Soda. 

With 
Sulphate 

of 
Ammonia. 

With 
Rape  Cake. 

6 

5 

Superphosphate  and  Potash  . 
Superphosphate  only 

Tons. 
29.6 
28.3 

Tons. 
28-2 
I2'0 

Tons. 

29-4 
14.9 

The  plots  receiving  potash  all  give  about  the  same 
yield,  whatever  the  source  of  nitrogen;  but  on  plots  5, 
without  potash,  the  yield  is  only  maintained  on  the 
nitrate  of  soda  plot ;  on  the  other  two  the  plant  is 
neither  supplied  with  potash  by  the  manure,  nor  is  the 
soil  forced  to  yield  some  of  its  stored-up  potash  as  it  is 
by  the  nitrate  of  soda,  whereupon  the  yield  declines  by 


II.] 


ACTION  OF  SODA  IN  NITRATE  OF  SODA 


53 


one-half  or  more.  For  twenty-five  years,  then,  the  use 
of  nitrate  of  soda  alone  has  enabled  the  soil  to  supply 
a  mangold  crop  with  the  large  amount  of  potash  it 
wants,  though  the  store  of  potash  in  the  soil  apparently 
soon  becomes  exhausted  when  a  manure  is  used  which 
cannot  bring  it  into  solution.  With  other  crops  the 
same  results  are  obtained,  though  the  lack  of  potash 
does  not  become  manifest  so  quickly  as  in  the  case  of 
mangolds.  For  example,  we  may  compare  the  yield  of 
barley  (Table  XI.)  for  successive  ten-year  periods,  the 
yield  of  each  plot  being  calculated  as  a  percentage  of 
that  on  the  completely  manured  plot  receiving  nitrate 
of  soda,  to  eliminate  seasonal  influences. 


Table  XL— Barley  Grain,  Hoosfield 

Rothamsted 

•    I 

^ 

^ 

ii  to 

V.  t~ 

t.  00 

f-  Oi 

t-  0 

g  M 

C3  CO 

CS  00 

03  00 

cj  c> 

Plot. 

>.lj 

^^ 

^3 

^S 

>.^ 

o  o 

0  i) 

■=>& 

oco 

0  Oi 

r-i  CO 

rt  00 

r-i  CO 

^^ 

^— ' 

'^ 

^^ 

'-' 

4N 

Nitrate,      Superphosphate, 

and  Potash     . 

lOOO 

1 00-0 

lOO-O 

lOO-O 

lOO-O 

2N 

Nitrate     and     Superphos- 

phate    .... 

98-0 

IOO-2 

99'S 

ios-7 

1 01 -4 

4A 

Ammonia,  Superphosphate, 

and  Potash     . 

92-4 

93-7 

97-2 

1007 

ico-8 

2A 

Ammonia   and  Superphos- 

phate    ,         •        .         . 

91.4 

97-8 

96-0 

908 

77-8 

It  will  be  seen  that  when  the  manure  contains 
potash  the  ammonium  salts  yield  practically  the  same 
crops  as  nitrate  of  soda.  When  the  nitrogenous 
manure  is  nitrate  of  soda,  the  omission  of  potash 
causes  no  diminution  in  the  yield  ;  but  with  ammonium 
salts  and  no  potash  the  crop  after  the  third  decade 
becomes  unable  to  satisfy  its  potash  requirements 
from  the  soil  alone,  and  the  yield  declines.  In  other 
words,  nitrate  of  soda  has  dispensed  with  the  necessity 


54        FERTILISERS  CONTAINING  NITROGEN     [chap. 

of  a  potash  dressing,  which  after  a  time  becomes 
necessary  when  sulphate  of  ammonia  is  the  nitrogenous 
manure. 

One  of  the  most  characteristic  effects  of  the  use 
of  nitrate  of  soda  as  a  manure,  either  repeatedly  or  in 
any  quantity,  is  its  deleterious  action  upon  the  texture 
of  a  heavy  soil ;  farmers  have  repeatedly  observed 
that  where  nitrate  of  soda  has  been  applied  the 
land  remains  very  wet  and  poaches  badly  if  it  is  at 
all  disturbed  before  it  has  dried.  Market  gardeners 
in  particular,  who  manure  heavily  with  nitrate  of 
soda,  have  found  this  destruction  of  the  tilth  a 
serious  drawback  to  its  use.  The  cause  has  usually 
been  put  down  to  the  hygroscopic  character  of  nitrate 
of  soda ;  since  the  salt  itself  readily  attracts  moisture 
from  the  air  and  will  even  liquefy  spontaneously,  it 
is  considered  that  it  keeps  the  land  moist  for  the 
same  reason.  But  the  extra  amount  of  moisture  that 
could  be  held  in  the  soil  by  a  few  hundredweights  of 
nitrate  of  soda  would  be  wholly  imperceptible  when 
distributed  through  the  hundred  tons  or  more  which 
the  top  inch  of  soil  weighs  per  acre,  even  if  the 
application  of  nitrate  of  soda  persisted  near  the 
surface  and  were  not  quickly  washed  down  in  the 
soil.  Some  of  the  Rothamsted  plots  in  the  mangold 
field,  where  very  large  amounts  of  nitrate  of  soda 
have  been  applied  year  after  year  for  the  last  fifty 
years,  show  this  deterioration  of  tilth  in  very  marked 
fashion,  the  land  being  intolerably  sticky  after  rain 
and  drying  into  hard  intractable  clods,  so  much  so 
that  it  is  very  difficult  to  secure  a  plant  of  roots  unless 
the  season  is  favourable.  Determinations,  however, 
of  moisture  in  the  surface  soil  do  not  show  any  sensible 
difference  between  these  plots  of  bad  texture  and  those 
v/orking  more  kindly,  so  that  we  must  put  aside  the 


Fig.  2. — Deflocculating  Action  of  Nitrate  of  Soda  on  Clay  Soils, 

he  jars  contain  water  in  which  equal  amounts  of  clay  soil  had  been  suspended  and 
allowed  to  settle  for  forty-eight  hours.  The  soil  in  the  left-hand  jar  had  been 
taken  from  a  plot  regularly  receiving  nitrate  of  soda. 


II.]  ACTION  OF  NITRATE  OF  SODA  ON  CLAY  SOILS  55 

idea  that  there  is  any  direct  attraction  of  water  by 
nitrate  of  soda  remaining  in  the  soil.  The  explanation 
appears  to  be  more  complex.  When  a  plant  is  feeding 
upon  a  neutral  salt  like  nitrate  of  soda,  it  takes  up 
rather  more  of  the  nitric  acid  than  of  the  soda,  leaving 
behind  in  the  soil  some  of  the  soda  combined  with 
carbonic  acid  excreted  from  the  root.  Water  cultures 
in  which  plants  are  grown  with  nitrate  of  soda  will 
actually  become  alkaline  to  test-paper  from  this  cause. 
Now,  a  very  small  quantity  of  a  free  alkali,  like  carbonate 
of  soda,  has  an  altogether  disproportionate  effect  upon 
clay ;  the  clay  is  deflocculated — i.e.,  the  little  aggregates 
of  very  fine  particles  which  cause  the  clay  to  crumble 
down  when  dry  and  to  allow  water  to  drain  through 
it,  are  immediately  resolved  into  their  finest  state  of 
division,  and  all  the  characteristic  properties  of  clay  are 
accentuated.  Deflocculation  is  effected  mechanically 
whenever  clay  is  puddled  or  worked  in  a  wet  con- 
dition, and  all  the  features  of  puddled  clay,  which 
is  both  retentive  of  water  and  impermeable  by  it, 
which  shrinks  greatly  in  drying  and  then  holds  together 
with  extreme  tenacity,  are  found  in  these  soils  when  the 
deflocculation  has  been  brought  about  by  a  little  dissolved 
alkali.  The  fact  that  such  deflocculation  has  taken 
place  may  be  illustrated  by  a  very  simple  experiment. 
Fig.  2  shows  two  large  jars,  each  containing  3 
litres  of  distilled  water,  in  which  has  been  shaken  up 
I  gramme  of  the  Rothamsted  clay  loam,  in  the  one 
case  from  a  plot  manured  with  nitrate  of  soda,  in 
the  other,  from  the  adjoining  plot  receiving  ammonium 
salts.  It  is  obvious  how  much  greater  is  the  amount 
of  material  remaining  suspended  in  the  jar  con- 
taining soil  manured  with  nitrate  of  soda,  which 
means  that  this  latter  soil  had  been  previously 
brought  into  a  more  fine-grained  and  less  flocculated 


56         FERTILISERS  CONTAINING  NITROGEN     [CHAP. 

condition.  Collateral  evidence  is  furnished  by  some 
of  the  other  Rothamsted  plots ;  for  example,  when 
the  tile  drains  beneath  the  wheat  plots  run,  the  water 
percolating  from  below  the  nitrate  of  soda  plot  is 
always  slightly  turbid  with  fine  suspended  clay  material, 
while  the  water  from  the  other  plots  is  clear.  This 
removal  of  the  finest  material  from  the  nitrated  plot 
has  been  so  persistent  during  the  fifty  years  or  so  of 
experiment  on  this  field,  that  the  mechanical  analysis  of 
the  soil  now  shows  a  smaller  proportion  of  clay,  which 
removal  has  only  been  possible  because  of  the  defloc- 
culation  brought  about  by  the  nitrate  of  soda  manuring. 
Again,  the  soil  of  the  plots  receiving  nitrate  of 
soda  is  found  to  be  losing  carbonate  of  lime  to  the 
water  percolating  through  it  at  a  lower  rate  than  the 
soil  of  the  unmanured  plot ;  this  is  because  the  pro- 
duction of  a  free  base  by  the  plant's  own  growth  has, 
to  a  certain  extent,  saved  the  carbonate  of  lime  in  the 
soil  from  attack.     The  following  table  (XII.)  shows  the 

Table  XII. — Calcium  Carbonate  in  Broadbalk  Wheat  Soils. 
First  Depth  (i  to  9  Inches). 


Plot. 

Per  cent,  in 
Fine  Dry  Soil. 

Loss 
per  Acre 

per 
annum. 

Lb. 

1865. 

1904. 

3 
9 

7 

2 

Unmanured 

Complete  Minerals  and  275  lb.  Nitrate 
of  Soda 

Complete  Minerals,  and  400  lb.  Am- 
monium Salts     ..... 

Dung 

4-54 
4-24 
3-82 

4-20 

3-29 

3-36 
2.25 

3-28 

800 

564 
lOIO 

590 

annual  average  rate  of  loss  of  carbonate  of  lime  for  the 
last  forty  years  from  some  of  the  chief  plots  of  the 
Broadbalk  field ;  it  will  be  seen  that  the  nitrate  of 
soda  has  reduced  the  loss  of  carbonate  of  lime  from  the 


II.]  NITRATE  OF  SODA   USED  ALONE  57 

soil  by  between  200  and  300  lb.  per  acre  per  annum, 
this  quantity  representing  the  base  it  has  itself  sup- 
plied. The  bad  texture  of  the  land  induced  by  the 
use  of  nitrate  of  soda  is  not  easily  removed ;  lime  is 
of  no  service  in  this  case,  because  it  only  adds  another 
alkali ;  a  better  remedy  is  to  be  found  in  the  simultaneous 
application  of  an  acid  manure  like  superphosphate. 
Better  still,  when  an  active  nitrogenous  manure  is 
needed,  instead  of  nitrate  of  soda  alone  a  mixture  of 
sulphate  of  ammonia  with  nitrate  of  soda  might  be 
employed ;  for,  as  will  be  seen  later,  sulphate  of 
ammonia  acts  on  soil  like  an  acid,  hence  a  mixture 
of  the  two  manures  ought  to  make  a  better  source  of 
nitrogen  than  either  alone. 

Amongst  farmers  a  certain  amount  of  prejudice 
against  nitrate  of  soda  still  lingers ;  it  is  described  as 
a  "  stimulant,"  even  as  a  "  scourge,"  and  is  regarded  as 
producing  a  crop  to  the  detriment  of  the  fertility  of  the 
land.  To  a  certain  extent  it  is  true  of  nitrate  of  soda, 
as  of  an}'  other  fertiliser  containing  only  a  single  con- 
stituent of  a  plant  food,  that  its  continued  use  alone 
must  increase  the  draft  upon  the  other  nutritive  elements 
in  the  soil,  in  this  case  phosphoric  acid  and  potash. 
Nitrate  of  soda,  also,  is  such  an  active  source  of  nitrogen 
and  nitrogen  is  so  dominant  a  factor  in  producing  growth 
that  large  crops  can  often  be  grown  for  a  time  by  the 
help  of  nitrate  of  soda  alone.  But  so  far  from  nitrate 
of  soda  being  specially  harmful  in  this  way,  the  Rotham- 
sted  experiments  show  that  the  yield  of  any  crop  is 
maintained  with  nitrate  of  soda  alone  better  than  with 
any  other  single  manure.  For  example,  the  produce  of 
mangolds  with  nitrate  of  soda  alone  averages  10^  tons 
for  twenty-seven  years,  as  against  10  tons  with  rape 
cake  alone,  and  under  6  tons  with  ammonium  salts 
alone.     But,  of  course,  the  true  answer  to  such  criticism 


58        FERTILISERS  CONTAINING  NITROGEN     [CHAP 

is  that  nitrate  of  soda  requires  to  be  used  with  phos- 
phates and  potash  in  order  to  make  up  a  complete 
fertiliser,  and  that  only  in  this  way  can  the  fertility  of 
the  soil  be  maintained.  As  has  already  been  seen, 
potash  can  generally  be  omitted  in  practice,  but 
phosphates  must  be  added  except  in  the  special  cases 
when  only  a  nitrogenous  manure  is  needed,  as  in  top 
dressings  for  wheat.  The  prejudice  against  nitrate  of 
soda  is  probably  really  due  to  its  injurious  effect  upon 
the  tilth ;  if  it  is  used  in  large  quantities  or  repeatedly, 
not  only  does  the  humus  content  run  down  but  the  land 
begins  to  work  badly,  so  that  poor  crops  result,  although 
the  land  has  not  been  particularly  exhausted  of  plant  food. 

As  a  fertiliser  the  special  value  of  nitrate  of  soda 
lies  in  its  immediate  availability ;  no  change  has  to  take 
place  before  it  passes  into  the  plant ;  in  consequence,  it 
has  a  very  immediate  effect  in  early  spring,  when  the 
land  is  still  so  cold  that  the  production  of  nitrates  by 
bacterial  processes  is  almost  suspended  however  rich 
the  soil.  As  an  aid  to  the  rapid  production  of  spring 
vegetables,  or  to  give  a  start  to  a  field  of  spring  corn 
dwindling  in  the  cold  east  winds,  or  to  push  a  crop 
through  an  insect  attack,  nitrate  of  soda  is  without  a 
rival. 

The  great  rival  of  nitrate  of  soda  is  at  present 
sulphate  of  ammonia,  of  which  over  200,000  tons  are 
annually  produced  in  this  country.  The  source  of 
origin  is  coal,  which  contains  about  1-5  to  2  per  cent,  of 
nitrogen  derived  from  the  original  vegetable  matter 
giving  rise  to  the  coal.  When  coal  is  subjected  to  any 
destructive  distillation  by  heat,  as  in  the  process  of 
gas-making  or  even  when  it  is  burnt,  about  15  per 
cent,  of  its  nitrogen  is  given  off  as  ammonia,  which  may 
be  recovered  from  the  gases  by  simply  washing  them 
with  water.     The  ammoniacal  gas  liquor  thus  produced 


II.] 


SULPHATE  OF  AMMONIA 


59 


is  redistilled  into  sulphuric  acid  and  sulphate  of 
ammonia  is  crystallised  out;  the  resulting  commercial 
salt  contains  about  20-5  per  cent,  of  nitrogen.  Not  only 
gas  works,  but  blast  furnaces,  coke  ovens,  shale  oil 
works,  etc.,  are  now  arranged  to  recover  this  valuable 
product  of  the  coal,  and  the  accompanying  table  shows 
the  current  output  from  each  of  these  sources  : — 


Table  XIII.— Production  of  Sulphate  of  Ammonia  in  the 
United  Kingdom. 


SCMlIVft. 

1901. 

1000. 

1899. 

Gas  works  .... 
Iron  works           ,         « 
Shale  works         .         « 
Coke,  etc.,  works 

Tons. 

148,500 
16,000 
36,500 
19,000 

Tons. 
142,000 
17,000 
37.000 
17,000 

Tons. 
134,000 
18,000 
38,500 
15,000 

Total  production    . 

220,000 

213,000 

205,500 

Exports       .... 
Home  consumption     . 

150,203 
69,797 

145,285 
67,715 

140,371 
65,129 

Average  price 

;^io,  IIS.  4d. 

;^ii,  2s.  od. 

;^ii,  5s.  lod. 

In  the  early  days  of  the  industry  hydrochloric  acid 
was  sometimes  employed,  in  which  case  ammonium 
chloride  (muriate  of  ammonia)  was  obtained,  but  the 
only  salt  now  prepared  as  a  manure  is  the  sulphate. 

Sulphate  of  ammonia,  when  pure,  is  a  white  crystal- 
line salt  freely  soluble  in  water  ;  the  commercial  article 
varies  somewhat  in  colour,  being  generally  grey  or 
yellow  from  a  trace  of  tarry  matter ;  in  some  cases  it  is 
distinctly  blue,  owing  to  the  presence  of  a  little  ferro- 
cyanide,  derived  from  the  cyanides  always  present  in 
coal-gas.  The  pure  salt  contains  21-2  per  cent,  of 
nitrogen,  and  as  the  commercial  article  is  generally  of 


6o        FERTILISERS  CONTAINING  NITROGEN     [chap. 

about  95  per  cent,  purity,  it  is  usually  guaranteed  to 
contain  20-2  per  cent,  of  nitrogen,  or  24-5  per  cent,  of 
ammonia.  Adulterations  are  infrequent  and  can 
readily  be  detected,  because  sulphate  of  ammonia  is 
the  cheapest  substance  which  is  wholly  volatile.  A 
handful  of  sulphate  of  ammonia  placed  on  a  fire  shovel 
and  heated  to  redness  over  a  fire  should  leave  no 
appreciable  residue.  Samples  of  the  salt  are  occasion- 
ally found  containing  ammonium  sulphocyanide  (thio- 
cyanate),  a  substance  actively  injurious  to  vegetation. 
Its  presence  can  be  readily  detected  by  adding  to  a 
solution  of  the  salt  a  little  ferric  chloride,  with  which  a 
sulphocyanide  produces  an  intense  red  coloration.  Like 
all  salts  of  ammonia,  the  sulphate  reacts  with  lime  and 
even  with  carbonate  of  lime,  giving  off  free  ammonia  as 
a  gas.  For  this  reason  sulphate  of  ammonia  should 
never  be  mixed  with  lime  or  with  basic  slag,  which 
contains  a  certain  amount  of  free  lime,  lest  a  loss  of 
nitrogen  should  ensue.  A  lightly  calcareous  soil  in  dry 
weather  may  induce  a  similar  loss  of  free  ammonia. 

As  a  nitrogenous  manure  sulphate  of  ammonia  is 
practically  as  effective,  nitrogen  for  nitrogen,  as  nitrate 
of  soda ;  it  is  also  to  all  intents  and  purposes  as  rapid 
in  its  action,  because  the  process  of  nitrification,  which 
generally  precedes  the  utilisation  of  the  ammonia  by  the 
plant,  takes  place  very  rapidly  in  suitable  soils.  The 
fact  is  well  illustrated  in  the  following  table  (XIV.), 
showing  the  composition  of  the  water  draining  from  one 
of  the  Rothamsted  wheat  plots  to  which  a  mixture  of 
sulphate  and  chloride  of  ammonia  had  been  supplied  on 
25th  October,  followed  the  next  day  by  heavy  rain,  so 
that  on  the  27th  the  drains  began  to  run.  It  will  be 
seen  that  at  this  early  date  the  ammonia  had  not  been 
wholly  caught  up  by  the  soil,  so  that  a  little  found  its 
way  into  the  drains;  at  the  same  time,  however,  the 


II.]   NITRIFICATION  OF  SULPHATE  OF  AMMONIA   6i 

proportion  of  nitrate  has  been  enormously  increased, 
due  to  immediate  nitrification,  and  the  later  runnings 
of  the  drains  in  November  and  December  show  that  the 
ammonium  salts  were  being  rapidly  oxidised  and  re- 
moved from  the  soil  as  nitrates. 

Table  XIV.— Broadbalk  Wheat  Field,  Rothamsted.  Nitrogen 
AND  Chlorine  in  Drainage  Water  from  Plot  15.  Parts 
per  Million. 


§5 

C3   ^ 

52§ 

Year. 

Month. 

Nitrogei 
Ammun 

5 

III 

1880 

October  10 

None 

8-2 

22-7 

37 -o 

1880 

October  27,  6-30  A.M. 

9-0 

13-5 

146-4 

9.2 

:    1880 

October  27,  i  P.M.     . 

6-5 

12.9 

II  6.6 

ii-i 

!    1880 

October  28 

2-5 

1 6-7 

95-3 

17-5 

1880 

October  29         .         .         . 

1-5 

i6-9 

80.8 

20-9 

:   1880 

November  15,  16 

None 

50-8 

54-2 

93-7 

I    1880 

November  19,  26 

None 

34-6 

47.6 

72.7 

:  1880 

December  22,  29,  30 . 

None 

21.7 

23-2 

93-5 

I88I 

February  2,  8,  10 

None 

22.9 

19.4 

ii8-o 

When  applied  to  the  soil  sulphate  of  ammonia  is 
very  rapidly  and  completely  absorbed ;  the  instance 
quoted  above  (Table  XIV.)  being  one  of  the  very  few 
cases  when  ammonium  salts  have  been  found  in  the 
waters  draining  from  the  Rothamsted  wheat  field, 
however  recent  the  application  of  ammonium  salts 
had  been.  The  sulphuric  acid  or  chlorine  is  found 
at  once  in  the  drainage  water,  but  combined  with 
calcium  and  magnesium  derived  from  the  soil.  It  is 
commonly  supposed  that  the  reaction  taking  place  is 
one  of  double  decomposition  with  the  calcium  carbonate 
in  the  soil — 

CaC0,  +  (NH4),S0,   =   (NH,).,C03  +  CaS0„ 


the  ammonium  carbonate  beinsf  held  without  further 


62        FERTILISERS  CONTAINING  NITROGEN     [CHAP. 

change  by  the  humus  in  the  soil.  But  experiments 
with  pure  kaolin  and  samples  of  natural  humus — peats 
of  various  age  and  origin — show  that  the  reaction  which 
takes  place  is  one  of  double  decomposition  whereby 
ammonium  displaces  calcium  and  magnesium  in  clay 
and  humus.  With  kaolin  and  clays  the  reaction 
takes  place  with  the  double  hydrated  silicates  or 
zeolites,  with  humus  with  certain  natural  calcium  com- 
pounds of  the  insoluble  complex  organic  humic  acids 
produced  during  decay.  A  certain  amount  of  the 
ammonia  is  also  taken  up  at  once  by  soil  bacteria  and 
converted  into  more  organised  and  insoluble  forms  like 
proteins. 

It  is  the  calcium  carbonate  in  the  soil  that  finally 
suffers  loss,  because  before  nitrification  takes  place  the 
ammonium  compounds  just  described  have  to  be 
decomposed  by  calcium  carbonate  with  the  produc- 
tion of  ammonium  carbonate,  which  alone  can  be 
attacked  by  the  nitrification  organisms. 

Referring  again  to  the  analyses  of  the  Rothamsted 
wheat  soils,  p.  56,  it  will  be  seen  that  the  long  con- 
tinued use  of  ammonium  salts  has  reduced  the  proportion 
of  calcium  carbonate  below  that  of  the  unmanured  plots 
by  amounts  which  are  approximately  those  to  be 
expected  if  interaction  between  the  salts  and  the  calcium 
carbonate  had  taken  place  according  to  the  equation  set 
out  above. 

The  Rothamsted  wheat  soils  started  with  sufficient 
calcium  carbonate  to  withstand  this  loss,  but  on  soils 
initially  poor  in  calcium  carbonate  its  removal  by 
sulphate  of  ammonia  soon  induces  a  condition  approach- 
ing actual  sterility.  The  best  example  is  afforded  by 
the  experimental  plots  on  the  farm  of  the  Royal 
Agricultural  Society  at  Woburn,  where  through  the  con- 
tinued .  use  of  ammonium    salts    as   manure,  the   soil 


II.]       ACIDITY  CAUSED  BY  AMMONIUM  SALTS       63 

refuses  to  grow  barley  any  longer,  though  the  former 
fertility  is  at  once  restored  by  the  application  of  a 
dressing  of  lime.  The  soil  of  the  plots  receiving 
ammonium  salts  is  actually  acid  to  litmus  paper,  and  a 
similar  condition  prevails  on  some  of  the  grass  plots 
at  Rothamsted,  where  the  soil,  unlike  that  of  the 
wheat  field,  is  deficient  in  calcium  carbonate.  At 
Woburn  the  soil  is  a  light  sandy  loam  which  con- 
tained in  1876,  when  the  experiments  began,  only 
0-074  per  cent,  of  calcium  carbonate.  For  many  years 
the  wheat  and  barley  plots  manured  with  ammonium 
salts  gave  as  good  returns  as  those  receiving  an  equal 
amount  of  nitrogen  as  nitrate  of  soda.  Towards  1895 
it  became  every  year  more  difficult  to  obtain  a  plant 
of  barley  on  the  plots  receiving  ammonium  salts,  the 
soil  was  noticed  to  be  acid  to  litmus  paper,  and  certain 
special  weeds,  spurry  in  particular,  invaded  the  plots. 
The  plots  were  then  divided,  and  on  one  portion  2 
tons  per  acre  of  lime  were  applied,  whereupon  the 
soil  recovered  its  healthy  condition  and  the  crop  was 
restored. 

Table  XV.  shows  the  result  on  the  crop  of  1904 
of  the  dressing  of  lime  applied  in  December  1897, 
and  also  the  destruction  of  the  crop  where  the 
soil  had  remained  acid  through  the  use  of  ammonium 
salts. 

The  effect  of  sulphate  of  ammonia  upon  wheat  at 
Woburn  is  not  so  marked  as  upon  barley,  probably 
because  of  the  deeper  rooting  habit  and  more  robust 
constitution  of  the  wheat  plant. 

The  acidity  of  the  soil  where  the  ammonium  salts 
have  been  used  is  due  to  the  attack  of  various  moulds 
and  other  micro-fungi  upon  the  ammonium  salts ;  they 
seize  upon  the  nitrogen  for  their  own  nutrition,  and  set 
free  the  acids  with  which  the  ammonia  was  combined.     If 


64        FERTILISERS  CONTAINING  NITROGEN     [chaP. 

there  is  no  calcium  carbonate  present  to  neutralise  the 
acids,  they  combine  with  the  calcium  of  the  humus  and 
set  free  humic  acid,  which  accumulates  from  year  to  year, 
until,  with  the  small  amount  of  mineral  acid  from  the 
salts  that  is  also  left  free,  the  acidity  becomes  consider- 
able enough  to  be  detected.  But  the  injury  to  the 
crop  seems  to  be  less  due  to  the  direct  effect  of  the 

Table  XV.— Woburn.    Yield  of  Barley,  1904. 


Bushels  per  Acre. 

No  Lime. 

After 
Liming. 

Ammonium  Salts  alone  (41  lb.  N.  per  acre) . 
Nitrate  of  Soda  alone  (41  lb.  N.  per  acre)     . 
Minerals  +  Ammonium  Salts  (4 1  lb.  N.  per  acre)  . 
Minerals  +  Nitrate  of  Soda  (41  lb.  N.  per  acre)     . 

0-7 

1-8 
247 

14-3 
23-9 

acids  upon  the  plant  than  to  the  way  the  acidity  tends 
to  suspend  the  normal  bacterial  activities  of  the  soil,  as, 
for  example,  the  process  of  nitrification,  and  to  replace 
them  by  the  growth  of  moulds  and  fungi.  In  the  acid 
grass  soils  at  Rothamsted,  for  example,  nitrification 
is  almost  at  a  standstill,  the  organisms  are  very  few 
in  number,  and  the  plant  is  chiefly  feeding  on  the 
unchanged  ammonia  of  the  manure. 

Although  under  ordinary  farming  conditions  an 
actually  acid  reaction  is  not  likely  to  arise  through  the 
use  of  sulphate  of  ammonia,  the  experiments  at  Woburn 
and  Rothamsted  clearly  indicate  that  it  is  not  a  desirable 
source  of  nitrogen  for  soils  which  are  deficient  in 
calcium  carbonate.  The  reaction  of  ammonium  salts 
with  the  soil,  resulting  in  the  withdrawing  of  the 
ammonia  from  solution,  gives  a  clue  to  the  difference 
in  both  the  yield  and  the  character  of  the  crop  when 


II.]  NITRATE  OF  SODA— SULPHATE  OF  AMMONIA  65 

grown  with  sulphate  of  ammonia  and  nitrate  of  soda 
respectively.  On  the  grass  plots  at  Rothamsted,  for 
example,  where  the  manuring  has  now  been  repeated 
year  after  year  for  fifty  years,  very  distinct  types  of 
herbage  have  associated  themselves  with  the  two 
manures.  Putting  aside  the  prevalence  of  sorrel  as 
due  to  the  acid  conditions,  the  characteristic  grasses  on 
the  plots  receiving  ammonium  salts  possess  a  shallow- 
rooted  habit,  e.g.,  sheep's  fescue  and  sweet  vernal  grass, 
while  the  nitrate  of  soda  has  favoured  deeply  rooting 

Table  XVI.— Ammonium  Salts  v.  Nitrate  of  Soda,  Rothamsted. 


Average  Yield. 

Wheat 
(22  years). 

Barley 
(51  years). 

Mangolds 
(i;7  years). 

Complete  Manure  :— 
Nitrogen  as  Nitrate 
„          „  Ammonia 

Bushels. 

28-7 
23-4 

Bushels. 

43-5 
42.1 

Tons. 

I8-OI 
14-86 

grasses  like  the  soft  brome.  Actual  examination  of 
the  subsoil  shows  that  the  roots  have  penetrated  much 
deeper  on  the  nitrate  of  soda  than  on  the  ammonia 
plots,  the  roots  having  followed  the  soluble  nitrate 
down  into  the  soil  in  the  one  case,  whereas  in  the  other 
they  remain  near  the  surface  where  the  nitrogenous 
material  has  been  accumulated.  We  may  apply  the 
clue  thus  obtained  to  interpret  the  comparative  results 
given  by  the  two  manures  on  other  crops ;  wheat,  for 
example,  a  deep-rooted  crop,  may  be  contrasted  with 
barley,  which  feeds  near  the  surface,  but  agrees  again 
with  mangolds,  another  deep-rooted  crop. 

It  will  be  seen  that  with  the   deep-rooting   crops, 
wheat  and  mangolds,  nitrogen  in  nitrate  of  soda  gives 


66        FERTILISERS  CONTAINING  NITROGEN     [chap. 

a  better  return  than  an  equivalent  amount  of  nitrogen 
in  ammonium  salts,  although  no  other  disturbing 
factors,  such  as  lack  of  potash  or  lime,  intervene  in  the 
cases  quoted  ;  with  barley,  however,  the  yield  is  sensibly 
equal  from  the  two  manures.  At  the  time  of  harvest, 
the  crop  grown  with  ammonium  salts  is  always  a  little 
the  riper ;  in  the  case  of  barley,  this  is  of  distinct  value, 
for  it  results  in  a  more  uniform  product  of  higher  quality. 
Taking  an  average  of  fourteen  years'  valuations  of  the 
barleys  grown  on  the  Rothamsted  plots,  the  corn  grown 
with  minerals  and  ammonium  salts  was  valued  at  104-3, 
while  the  produce  from  minerals  and  nitrate  of  soda  was 
set  at  100-3,  ^^id  that  from  the  plot  receiving  farmyard 
manure  at  96-4  only,  100  being  the  average  price  of 
barley  for  the  year.  These  figures  are  calculated  from 
the  cash  valuations  put  on  the  various  barleys  every 
year.  With  the  mangolds  again,  it  is  seen  that  the 
plants  manured  with  nitrate  continue  to  grow  long 
after  those  manured  with  ammonium  salts  have  so 
completed  their  season's  growth  that  the  leaves  are 
beginning  to  turn  yellow  and  flaccid.  All  these 
differences  are  explained  by  the  deeper  rooting  habit 
induced  by  the  nitrate  ;  the  plant  is  less  affected  by 
the  drought  and  the  changes  of  temperature  incident 
to  autumn,  growth  is  more  prolonged,  with  the  cor- 
ollary of  a  larger  yield  but  a  later  and  less  uniform 
maturity. 

One  other  factor  may  also  contribute  to  the  general 
superiority  of  nitrate  of  soda.  It  must  not  be  forgotten 
that  when  a  nitrogenous  manure  reaches  the  soil  there 
will  be  competition  for  it  between  the  plant's  roots  and 
the  mass  of  living  organisms  present  in  the  soil,  nearly 
all  of  which  required  combined  nitrogen  for  their  own 
development.  Some  of  these  organisms,  like  the 
nitrification  bacteria,  are  wholly  useful.     Others  cause 


11.]  IVET  AND  DRV  SEASONS  67 

permanent  loss  by  liberating  some  of  the  nitrogen  in 
the  form  of  gas,  but  the  majority  simply  withdraw  the 
soluble  nitrogen  for  a  time  from  circulation,  building  it 
up  in  their  own  tissues.  The  immediate  result  is, 
however,  a  lessened  availability  of  the  manure,  and  this 
loss  will  fall  far  more  upon  ammonium  compounds  than 
upon  nitrates,  which  are  not  so  generally  utilisable  by 
the  organisms  found  in  the  soil. 

It  is  generally  assumed  that  since  nitrate  of  soda  is 
not  retained  by  the  soil,  while  ammonium  salts  are, 
the  former  is  a  manure  better  suited  to  dry  seasons  and 
climates,  whereas  under  wetter  conditions  there  is  less 
danger  of  the  latter  washing  out  of  the  soil.  This  view, 
however,  forgets  that  if  the  ammonium  salts  are  to  feed 
the  plant  they  must  be  nitrified,  and  that  the  calcium 
nitrate  produced  is  just  as  likely  to  be  washed  down  in 
a  wet  season.  Indeed,  the  Rothamsted  results  do  not 
bear  out  the  popular  idea.  In  exceptionally  dry  seasons 
there  may  be  some  advantage  from  the  use  of  nitrate 
of  soda  because  of  the  deep-rooted  habit  it  induces, 
but  the  advantage  is  still  more  pronounced  in  seasons 
of  excessive  wet.  Taking  an  average  of  the  wet  seasons 
against  the  dry,  the  ammonium  salts  do  better  in  the 
latter.  Probably  the  nitrification  of  the  ammonium  salts 
is  checked  in  wet  seasons  when  the  temperature  is  low, 
when  also  aeration  is  deficient  through  the  repeated 
saturation  of  the  soil. 

In  addition  to  the  definite  compounds  which  have 
just  been  described,  a  very  large  number  of  waste 
products  from  some  industrial  or  manufacturing  pro- 
cess dealing  with  material  containing  nitrogen  are 
employed  as  nitrogenous  manures.  For  example, 
almost  all  animal  products  contain  nitrogen,  hence  the 
residues  from  slaughter-houses,  fish-curing  sheds,  and 
other  processes  concerned  in  the  preparation  of  food. 


68        FERTILISERS  CONTAINING  NITROGEN     [chap. 

which  are  not  utilisable  in  other  ways,  are  available  for 
manure.  Again,  all  industries  dealing  with  wool,  silk, 
hair,  feathers,  skins,  give  rise  to  highly  nitrogenous 
waste  material,  and  other  residues  of  vegetable  origin 
occur  from  time  to  time. 

From  their  origin  and  mode  of  preparation  it  follows 
that  these  substances  must  be  of  very  variable  composi- 
tion :  again,  the  supply  is  apt  to  be  irregular  and 
limited,  so  that  their  use  is  somewhat  local  and  confined 
to  particular  classes  of  farmers. 

Most  of  the  manures  of  organic  origin  will  contain 
phosphoric  acid  as  well  as  nitrogen,  but  as  a  matter 
of  convenience  some  of  them  may  be  treated  as  purely 
nitrogenous  fertilisers,  leaving  others  to  be  dealt  with 
among  the  compound  substances. 

Of  these  waste  materials  the  most  generally  used 
is  soot ;  its  value,  which  is  due  as  much  to  its  physical 
effects  upon  the  soil  as  to  its  fertilising  constituents, 
has  been  known  for  the  last  three  centuries  at  least. 
It  has  already  been  pointed  out  that  coal  contains  one 
per  cent,  or  more  of  nitrogen ;  in  a  fire  some  of  this 
is  evolved  as  ammonia  when  the  coal  is  heated,  and  if 
it  escapes  combustion  in  the  higher  levels  of  the  fire  it 
is  afterwards  partially  arrested  by  the  particles  of  carbon 
constituting  soot,  which  possess  an  exceptional  power  of 
condensing  gases  upon  their  surface.  In  the  main  soot 
is  only  an  impure  form  of  carbon  ;  its  fertilising  value 
is  due  to  the  small  and  variable  proportion  of  ammonia 
it  has  thus  absorbed  from  the  gases  in  the  chimney. 
The  percentage  of  nitrogen  present  may  be  as  low  as 
0-5,  in  exceptional  cases  it  may  rise  to  6,  3-2  being  the 
mean  of  a  large  number  of  analyses. 

Since  the  nitrogen  is  present  in  the  form  of 
ammonia,  soot  as  a  fertiliser  may  be  regarded  as  one 
of  the  ammonium   salts ;    its  action,  however,  is  pro- 


II.]  SOOT  69 

foundly  modified  by  its  physical  condition.  In  the  first 
place,  the  dark  colour  of  soot  makes  it  a  very  effective 
absorbant  of  the  sun's  rays,  so  that  in  sunlight  the  tem- 
perature of  land  which  has  been  darkened  by  a  sprinkling 
of  soot  will  rise  two  or  three  degrees  above  that  of 
the  same  land  uncoloured.  And  as  the  radiation  from 
such  darkened  soil  at  low  temperatures  is  not  increased 
in  the  same  proportion,  there  is  no  corresponding  loss 
of  heat  at  night  from  the  sooted  land  to  discount  its 
higher  temperature  by  day.  Soot  is  most  commonly 
used  by  farmers  as  a  top  dressing  for  wheat  and  other 
spring  corn ;  these  crops  are  particularly  responsive 
to  a  small  application  of  active  nitrogenous  manure 
in  the  early  months  of  the  year  when  the  soil  is  cold 
and  the  oxidation  of  its  nitrogenous  residues  is  slow, 
hence  part  of  the  value  of  the  soot.  At  the  same  time, 
the  increased  temperature  of  the  soil  induced  by  the 
black  colour  of  the  soot  is  particularly  valuable  in 
forwarding  the  growth  both  of  the  plant  itself  and  of 
the  bacteria  which  are  rendering  available  the  reserves 
of  plant  food  in  soil. 

Soot  also  helps  materially  to  lighten  the  texture  of 
heavy  soils,  and  on  that  account  is  much  valued  by 
market  gardeners  in  districts  like  Evesham,  where  the 
land  is  somewhat  clayey  and  retentive. 

Soot  is  also  very  distasteful  to  the  slugs  and  small 
snails  which  often  do  great  damage  to  cereal  and  other 
crops  in  their  earlier  stages. 

Soot  is  usually  sold  by  the  bushel,  which  weighs 
about  28  lbs.,  and  the  lighter  the  soot  is  per  bushel 
the  more  it  is  valued,  because  this  indicates  its  purity 
and  freedom  from  ashes  or  other  admixture.  This  is 
probably  the  best  test  the  farmer  can  apply,  for  soot 
being  bought  locally  no  guarantee  can  be  obtained  as 
to  its  composition,  nor  could  one  very  well  be  given, 


^o       FERTILISERS  CONTAINING  NITROGEN     [chap. 

so  small  and  irregular  are  the  parcels  from  which  any 
bulk  of  soot  is  made  up. 

Another  group  of  substances  which  practically  are 
purely  nitrogenous  manures  are  the  shoddies  and  kindred 
products  derived  from  textile  industries  and  other  trades 
dealing  with  silk,  wool,  hair,  fur,  or  skin.  Properly 
speaking,  shoddy  should  consist  of  the  short,  broken 
fragments  of  wool  which  are  rejected  in  the  various 
processes  for  preparing  woollen  fabrics  because  they 
are  not  long  enough  to  make  up  into  yarn,  but  now 
the  term  is  applied  more  generally  to  any  form  of 
waste  from  silk  or  wool  manufacturing  which  is  no 
longer  profitable  to  work  up  for  cloth.  The  material 
is  thus  extremely  valuable  in  composition ;  pure  wool 
contains  over  17  per  cent,  of  nitrogen,  pure  silk  about 
as  much,  and  at  one  end  of  the  scale  of  shoddies  come 
materials  like  carpet  waste,  cloth  clippings,  and  gun  wad 
waste,  which  are  nearly  pure  and  may  contain  as  much 
as  14  per  cent,  of  nitrogen.  Less  valuable,  because  of 
the  greater  admixture  of  dirt,  are  wool  combings,  flock 
dust,  and  other  cloth  wastes  where  cotton  is  also  used, 
these  may  have  5  to  10  per  cent,  of  nitrogen  ;  while  lower 
still  come  the  manufacturing  dust  from  textile  factories, 
the  sweepings  of  workshops,  etc.,  in  which  the  nitrogen 
may  fall  as  low  as  3  per  cent. 

Closely  allied  to  such  shoddies  are  hair  and  fur 
waste,  skin  waste,  rabbit  flick  (ears,  tail,  feet,  etc.,  and 
other  fragments  of  rabbit  skins),  feathers,  ground  hoofs, 
horn  shavings,  and  leather  dust. 

In  all  these  materials  the  nitrogen  exists  in  very 
complex  compounds  of  carbon,  insoluble  in  water,  and 
requiring  to  pass  through  several  stages  of  bacterial 
decomposition  before  they  reach  the  plant.  In  conse- 
quence of  their  very  variable  composition  and  character 
it  is  impossible  to  make  any  general  statements  about 


II] 


NITROGENOUS  WASTE  MATERIALS 


71 


their  action  as  manures,  though  certain  principles  may 
be  laid  down.  In  the  main  they  are  slow  and  lasting 
manures,  akin  in  this  respect  to  the  more  resistant 
constituents  of  farmyard  manure,  but  the  rapidity  of 
their  action  will  depend  to  a  very  large  extent  upon 
the  fineness  of  their  division  and  to  the  warmth  and 
the  amount  of  cultivation  the  soil  receives.  Fine 
woollen  material  like  flock  dust,  rabbit  hair,  and  small 
feathers  decays  with  some  rapidity  in  the  soil,  and  give 
a  very  considerable  return  in  the  season  of  their  applica- 
tion, as  may  be  seen  from  the  following  table  of  results 
obtained  at  Rothamsted  with  a  fine  flock  dust  shoddy 
containing  i2-6  per  cent,  of  nitrogen.  In  the  table 
(XVII.)  the  results  of  four  years'  experiments  with 
different  crops  are  reduced  to  a  common  standard,  the 
unmanured  plot  each  year  being  reckoned  as  100,  and 
the  effect  of  the  manure  is  shown  for  the  four  successive 
crops  following  the  application  : — 

Table  XVII.— Value  of  Residues  from  Previous  Applications 
OF  Shoddy.     Rothamsted, 


Un- 
manured. 

Shoddy, 
same  year. 

Shoddy, 

previous 

year. 

Shoddy, 
2  years 
before. 

Shoddy, 
3  years 
before. 

Swedes 
Barley 
Mangolds 
Wheat       . 
Swedes 

Mean  . 

100 
100 

100 
100 
100 

I43-I 
i66-9 
140.8 
177-2 
130-7 

139-9 
136-9 

147-3 
146-9 

I2I-9 

io7'5 
126-6 

II0-4 
loS-l 

100 

152 

142 

119 

109 

Many  of  the  coarser  materials,  rags,  hair,  skin, 
may  be  found  in  the  soil  apparently  but  little  changed 
for  a  year  or  two  after  their  application ;  while  such 
coarse  and  tough  material  as  crushed  hoofs  and  leather 
waste  must  change  with  extreme  slowness,  and  can  be 


72        FERTILISERS  CONTAINING  NITROGEN     [chap. 

of  little  service  except  in  such  cases  as  vine  borders, 
where  the  prime  cost  is  not  of  very  great  moment  but 
the  land  has  to  remain  without  further  manuring  for 
many  years.  The  presence  of  oil  in  a  sample  of  shoddy 
is  generally  regarded  as  detrimental,  since  it  hinders 
the  access  of  water  and  so  delays  the  decomposition  of 
the  nitrogenous  material.  But  considering  how  rapidly 
all  oils  and  fats  are  attacked  by  bacteria,  it  is  doubtful 
if  this  objection  is  valid,  and  actual  experiments  are 
lacking. 

The  value  of  woollen  rags  as  manure  has  long  been 
known.  Blithe  wrote  in  1653  *  "Coarse  wool,  nippings, 
and  tarry  pitch  marks,  a  little  whereof  will  do  an  acre  of 
land,  there  is  great  virtue  in  them.  I  believe  one  load 
hereof  will  exceedingly  well  manure  half  an  acre,"  and 
at  the  beginning  of  the  nineteenth  century  Arthur 
Young  recommended  them  for  dry,  gravelly,  and  chalky 
soils.  At  the  present  day,  though  shoddy  is  used  to 
some  extent  in  general  farming  in  the  neighbourhood 
of  cloth-manufacturing  districts,  and  though  a  certain 
amount  is  worked  up  into  compound  manures,  it  is 
mainly  consumed  by  the  hop  and  fruit  growers.  Such 
farmers  are  dealing  with  a  perennial  crop,  the  quality  of 
which  is  important ;  in  consequence  they  prefer  a  nitro- 
genous manure  which  will  come  into  action  steadily  and 
continuously  throughout  the  season,  rather  than  an 
active  one  which  will  at  any  time  induce  a  sudden  rush 
of  growth.  As  the  plant  continues  on  the  same  ground 
year  after  year,  the  residues  of  slow-acting  manures 
which  are  not  recovered  in  the  first  crop  accumulate  in 
the  soil.  Eventually  the  land  becomes  stored  with 
manurial  residues,  which  come  into  action — i.e.,  decay 
and  nitrify — pari  passu  with  the  growth  of  the  plant, 
because  both  the  plant  and  the  soil  bacteria  are  similarly 
affected  by  the  variations  in  such  factors  as  warmth  and 


II.]  SHODDY  73 

ir.oisture.  The  result  of  the  continuous  and  steady 
feeding  of  the  plant  in  this  fashion  is  an  equable 
development,  which  is  found  to  give  rise  to  high 
quality  in  the  product. 

Hop  and  fruit  growers,  in  fact,  regard  shoddy  as  the 
best  substitute  for  farmyard  manure,  of  which  they  are 
rarely  able  to  make,  or  even  to  buy,  as  much  as  they 
require ;  for  fruit,  indeed,  shoddy  is  often  regarded  as 
preferable  to  farmyard  manure,  because  it  results  in 
healthier  growth.  The  organic  matter  present  in 
shoddy  is  of  value  in  improving  the  texture  and  water- 
retaining  power  of  the  soil,  and  i  to  2  tons,  according 
to  the  nitrogen  it  contains,  are  regarded  as  a  fair 
equivalent  for  20  tons  of  farmyard  manure,  though  the 
latter  will  supply  considerably  more  non-nitrogenous 
organic  matter.  Shoddy  is  only  suitable  for  arable 
land,  and  should  preferably  be  applied  in  the  early 
winter  and  ploughed  or  dug  in  as  soon  after  it  has 
been  spread  as  possible,  in  order  to  start  the  decay 
processes. 

The  inevitable  irregularity  in  the  composition  of 
shoddy,  even  in  the  output  from  week  to  week  from 
a  single  factory,  renders  its  sale  on  any  exact  basis 
a  matter  of  some  difficulty.  It  is,  indeed,  a  very 
unsatisfactory  task  to  obtain  a  sample  of  a  few  pounds 
which  will  properly  represent  the  bulk  of  a  consign- 
ment, and  the  difficulties  are  renewed  in  the  laboratory 
when  the  large  sample  has  to  be  reduced  to  a  few 
grammes  for  analysis.  When,  therefore,  shoddy  is  bought 
and  sold  on  a  guarantee,  a  somewhat  wide  margin  of 
variation  must  be  allowed ;  a  large  bulk  is,  perhaps, 
best  purchased  on  the  basis  of  a  given  price  per  unit  of 
nitrogen,  samples  being  drawn  from  each  consignment 
on  arrival  and  a  mean  taken  of  their  analyses  in  order 
to  fix  the  price.     While  nothing  but  an  analysis  will 


74        FERTILISERS  CONTAINING  NITROGEN     [chap. 

afford  a  definite  idea  of  the  quality  of  a  shoddy,  some 
opinion  can  be  formed  by  tearing  a  small  sample  to 
pieces  and  trying  each  portion  in  a  gas  or  candle  flame. 
Wool,  silk,  hair,  and  all  nitrogenous  materials,  frizzle 
up  and  burn  slowly  with  an  unpleasant  smell ;  cotton, 
linen,  and  similar  substances  of  no  fertilising  value,  burn 
quickly  with  a  clear  flame,  since  they  consist  when  pure 
of  cellulose.  Or  the  mass  may  be  digested  by  gentle 
heating  with  a  strong  solution  of  caustic  soda  or  potash, 
in  which  the  wool  and  kindred  substances  will  dissolve, 
leaving  untouched  the  cellulose  and  dirt.  But  analysis 
forms  the  only  real  basis  for  determining  the  richness  of 
the  material,  added  to  which  the  farmer  must  exercise  his 
own  judgment  about  its  fineness  and  the  possibility  of 
getting  it  properly  distributed  throughout  the  soil. 

Woollen  shoddies  are  sometimes  treated  with 
sulphuric  acid,  with  a  view  of  starting  the  decomposi- 
tion of  the  nitrogen  compounds  and  so  rendering  them 
more  quickly  available.  Shoddy  thus  treated  is  also 
used  as  a  source  of  nitrogen  in  making  various  com- 
pound and  mixed  manures.  Evidence  is,  however, 
lacking  that  the  sulphuric  acid  does  quicken  the  decay 
of  the  shoddy,  and  on  any  soils  but  those  rich  in  calcium 
carbonate  the  introduction  of  so  much  free  sulphuric 
acid  is  not  advisable. 

It  would  be  difficult  to  enumerate  all  the  bodies 
which  from  time  to  time  get  applied  to  the  land  as 
nitrogenous  manures :  tallow  chandlers'  waste  or 
"  greaves "  is  a  residue  containing  from  3  to  9  per 
cent,  of  nitrogen,  according  to  its  origin,  and  a  little 
phosphoric  acid ;  it  is  often,  however,  comparatively 
high  in  price,  because  the  better  qualities  are  saleable  as 
poultry  food. 

Spent  hops,  and  kiln  or  malt  dust  (the  rootlets  of 
the  germinated  barley  which  are  broken  off  when  the 


II] 


SEA  WEED 


75 


malt  is  dried)  are  sometimes  available,  and  the  latter  is 
a  valuable  and  active  manure  if  it  can  be  obtained 
cheaply. 

In  the  neighbourhood  of  the  sea  other  materials  can 
sometimes  be  obtained  ;  sprats  or  herrings,  when  a  glut 
renders  such  fish  unsaleable,  mussels,  and  starfish  or 
"  five  fingers  "  collected  from  the  oyster  beds,  are  all 
used  in  the  Kentish  hop  gardens,  and  the  two  latter 
supply  carbonate  of  lime  as  well  as  nitrogen.  Off  the 
south  and  west  coasts,  and  in  the  Channel  Islands, 
seaweed  forms  the  staple  manure,  being  collected  after 
heavy  weather  and  laid  up  in  heaps  to  dry  and  rot.  On 
the  heaviest  soils  it  is  sometimes  ploughed  in  immedi- 
ately after  gathering,  just  as  "  long "  dung  is  used  on 
clays  to  open  up  the  soil.  The  following  analyses 
(Table  XVIII.)  show  the  composition  of  three  different 
kinds  of  seaweed  used  for  manure  in  Jersey  : — 

Table  XVIII. — Analyses  of  Seaweed.    Russell. 


Fucus. 

Laminaria. 

Sea  Grass. 

Water 

Organic  matter  .... 
Containing  Nitrogen  .         .         , 

Ash 

Containing  Phosphoric  Acid 

„           Potash 

„           Sand 

30-5 
51-3 
1.56 

l8-2 

0-50 

4-5 
0-86 

52.8 

30-0 

0-7 

17-2 

0-43 

37 

0-54 

22-6 

59.1 
0-52 

18.3 
0-62 
0-56 

2-8 

Thus,  even  the  poorest  of  these  samples  is  in  its 
wet  condition  about  as  rich  as  the  ordinary  farmyard 
manure,  while  the  fucus  would  be  valued  as  highly  as 
£2  a  ton. 

These  results  are  probably  above  the  average ;  a 
number  of  samples  of  Fucus  from  the  North  Sea  gave 
only  0-3  to  0-4  per  cent,  of  nitrogen,  and  o-i  to  02  per 


76    FERTILISERS  CONTAINING  NITROGEN    [chap.  ii. 

cent,  of  phosphoric  acid,  while  species  of  Laminaria 
from  the  same  locality  contained  from  0-15  to  0-5  of 
nitrogen,  and  0-2  to  0-3  of  phosphoric  acid. 

It  is  needless  to  continue  the  enumeration  of  the 
substances  which  from  time  to  time  are  employed  as 
manures :  leather  in  the  form  of  dust,  turnings  and 
shavings  of  horn,  meat  and  cheese  that  have  been 
condemned  for  food,  all  find  their  way  from  time  to 
time  either  to  the  manure  manufacturer  or  to  the  land. 

The  only  general  rule  one  can  apply  to  such 
residues  is  to  buy  them  on  their  approximate  nitrogen 
content,  paying  a  low  unit  price  because  of  their  slow- 
ness of  action,  and  also  to  take  into  account  the 
comparative  fineness  of  division  and  ease  of  spreading. 
Even  the  most  resistant  material,  such  as  leather  or 
horn,  will  decay  if  it  is  only  freely  enough  divided  and 
disseminated  through  the  soil 


CHAPTER  III 

THE   FUNCTION   AND   COMPARATIVE   VALUE   OF 
NITROGENOUS   MANURES 

Nitrogen  promotes  the  Vegetative  Activity  of  the  Plant — Growth 
proportional  to  Nitrogen  Supply — With  Excess  of  Nitrogen 
Maturity  is  deferred  and  the  Proportion  of  Straw  to  Grain  is 
increased — Variation  of  Composition  of  Crop  with  Nitrogen 
Supply — Susceptibility  of  Plants  to  Disease  when  supplied 
with  Excess  of  Nitrogen — Crops  requiring  Large  Quantities 
of  Nitrogen — Relative  Availability  of  Nitrogenous  Manures — 
Nitrate  of  Soda  v.  Sulphate  of  Ammonia — Question  to  be 
decided  by  the  Nature  of  the  Soil — Residues  left  by  the 
Different  Nitrogenous  Manures — Greater  Value  attached  by 
Farmers  to  Manures  containing  Nitrogen  in  Organic  Com- 
bination. 

Before  passing  on  to  a  comparison  of  the  values  ot 
the  different  nitrogenous  manures,  it  is  necessary  to 
consider  how  far  nitrogen  exerts  on  the  plant  a  specific 
effect  that  shows  itself  whenever  there  is  either  an  excess 
or  defect  of  the  constituent  in  the  soil.  To  answer 
this  question  properly,  we  should  require  to  know  what 
is  the  physiological  function  of  nitrogen  in  the  nutrition 
of  the  plant,  and  though  we  are  still  far  from  any  full- 
ness of  knowledge,  certain  general  conclusions  may  be 
drawn  both  from  field  experiments  and  from  the  experi- 
ence of  the  farm.  In  the  first  place,  nitrogen  is  mainly 
concerned  with  the  vegetative  growth  of  the  plant,  with 
the  formation  of  leaf  and  stem  that  are  the  necessary 

77 


78  NITROGENOUS  MANURES  [chap. 

preliminaries  to  complete  development.  A  deficiency  of 
nitrogen  results  in  a  stunted  general  growth,  in  which 
the  grain  or  seed  bears  a  high  proportion  to  the  whole 
weight  of  the  crop;  the  plant  on  analysis,  however, 
shows  no  marked  lack  of  nitrogen  as  compared  with  the 
other  constituents.  These  other  bodies,  phosphoric 
acid,  potash,  etc.,  in  whatever  excess  they  may  be 
present  in  the  soil,  are  only  taken  up  by  the  plant  as  it 
can  use  them — i.e.,  in  quantities  proportionate  to  the 
growth,  which  in  its  turn  is  proportionate  to  the 
nitrogen  supply.  As  the  amount  of  available  nitrogen 
is  increased,  the  development  of  leaf  and  shoot  increases, 
their  green  colour  deepens,  and  maturity  becomes 
more  and  more  deferred,  so  that  a  crop  grown  on 
land  over-rich  in  nitrogen  always  tends  to  be  late 
and  badly  ripened,  and  to  show  a  profusion  of  leaf — 
characters  which,  in  the  case  of  a  grain  crop,  often 
result  in  lodging  before  harvest. 

But  the  fact  that  the  primary  growth  of  the  plant  is 
up  to  certain  limits  almost  proportional  to  the  supply 
of  nitrogen,  so  that  an  application  of  nitrogenous 
manure  has  a  quickly  visible  effect,  not  only  makes  it 
the  leading  constituent  of  a  fertiliser,  but  is  apt  to  give 
it  a  fictitious  importance  in  the  farmer's  eyes. 

On  most  of  our  cultivated  soils,  when  the  cropping  is 
continued  and  manure  withheld  to  a  point  when  there 
begins  to  be  a  serious  falling  off  in  the  yield  through 
lack  of  plant  food,  it  is  the  want  of  available  nitrogen 
rather  than  of  phosphoric  acid  and  potash  which 
determines  the  yield  ;  in  other  words,  the  soil  is  much 
more  rapidly  exhausted  of  its  available  nitrogen  than 
of  its  available  phosphoric  acid  and  especially  of  its 
available  potash.  Thus,  while  each  of  these  three  con- 
stituents of  plant  food  is  equally  indispensable  to  the 
plant,  good  crops  can  often  be  grown  by  the  aid  of  a 


III.]    IMPORTANCE  OF  NITROGENOUS  MANURES   79 


nitrogenous  manure  alone,  and  in  nearly  all  cases  by  a 
mixture  of  nitrogenous  and  phosphatic  manures.  The 
special  value  of  nitrogen  in  this  connection  is  well  seen 
in  the  Rothamsted  experiments  ;  on  the  wheat  field,  for 
example,  we  may  compare  the  yield  of  the  unmanured 
plot  with  that  receiving  nitrogen  alone  and  minerals 
alone,  and  again  that  which  receives  nitrogen  and 
phosphoric  acid  against  that  which  receives  nitrogen, 
phosphoric  acid,  and  potash. 

From  Table  XIX.  it  will  be  seen  that  plot  5,  which 
is  nitrogen  starved  but  which  receives  an  excess  of  all 
the  other  elements  of  nutrition,  only  yields  1-9  bushels 

Table  XIX.— Average  Yield  of  Wheat.    Broadbalk, 
Rothamsted.    56  years  (1852-1907). 


Plot. 

Grain. 

Straw. 

3 

5 

10 

II 

13 

Unmanured 

Mineral  Manures  only,  no  Nitrogen 
Nitrogen  only,  no  Minerals     . 

,,         and  Phosphates 

„         Phosphates,  and  Potash   . 

Bushels. 
12-9 

14-8 

20-5 

237 

31-6 

Cwts. 
IO-5 

12-3 

18.7 

22-8 

31-9 

more  grain  than  the  unmanured  plot ;  whereas  plot  10, 
which  receives  an  excess  of  nitrogen  but  has  had  to 
rely  solely  upon  the  original  reserves  of  minerals  in 
the  soil,  has  produced  on  the  average  7-6  bushels  of 
corn  more  than  the  unmanured  plot.  The  minerals  only 
increased  the  yield  by  14-7  per  cent,  but  nitrogen  by  59 
per  cent,  and  these  differences  would  have  been  much 
more  pronounced  had  they  been  calculated  on  the 
results  of  the  first  year  or  two  of  the  experiments  only, 
instead  of  over  a  period  so  long  that  the  mineral  reserves 
of  the  soil  are  also  highly  exhausted.  It  is  this  greater 
relative  deficiency  of  available  nitrogen  than  of  available 


8o 


NITROGENOUS  MANURES 


[CHAP. 


potash  or  phosphoric  acid  in  the  soil  which  makes  the 
nitrogenous  compounds  the  most  important  manures  in 
practice,  though  in  the  formation  of  this  opinion  some- 
thing also  must  be  set  down  to  the  fact  than  an  applica- 
tion of  nitrogenous  manure  always  shows  itself  in  the 
richer  green  colour  and  increased  vigour  of  the  plant, 
whereas  the  effect  of  phosphatic  manures  is  generally 
only  to  be  ascertained  from  the  weight  of  the  ripe 
product  like  the  grain. 

Another  result  of  the  amount  of  mineral  reserves  in 
the  soil  is  that  crops  such  as  wheat  or  mangolds,  which 
are  chiefly  dependent  upon  an  external  supply  of  nitro- 
gen, give  yields  that  are  roughly  proportional  to  the 
amount  of  nitrogen  supplied  as  long  as  it  is  not  large  ; 
there,  however,  soon  comes  a  point  when  the  law  of 
diminishing  returns  comes  into  play  and  the  return 
for  each  further  addition  of  nitrogen  falls  off  rapidly. 
The  following  table  (XX.)  taken  from  the  Rothamsted 

Table  XX. — Wheat  with  Increasing  Amounts  of  Nitrogen. 
Broadbalk,  Rothamsted.    (Average,  1852-1864.) 


Plot. 

Manures. 

11 

a      m 

1-H          ,, 

Grain. 

0  ^ 

Bushels. 

Wt.  per 
Bushel. 

5 
6 

7 

8 

16 

Minerals  only 
+  43  lb.  N,  . 
+   86      „       . 
+  129      „       . 

+  172      „      . 

Lb. 
3009 
4829 
6601 
7234 
7713 

1820 

1772 

633 

479 

18.3 
28-6 
37-1 
39-0 
39-5 

58-2 
58-9 
58-7 
58-2 
58-0 

16-6 
27.1 
38-1 
42.7 
46-6 

62-0 
58-9 
54-6 
Si-3 
47-9 

experiments,  illustrates  this  in  regard  to  wheat ;  there 
are  five  plots  each  receiving  the  same  phosphoric  acid 
and  potash,  in  excess  of  the  crops'  requirements,  but 
the  supply  of  nitrogen  increases  by  regular  steps  from 
none  to  172  lb.  per  acre. 


in.]        YIELD  WITH  INCREASING  NITROGEN  8i 

Considering  the  total  produce  as  a  measure  of  the 
growth,  it  will  be  seen  that  the  increase  produced  by 
the  second  43  lb.  of  nitrogen  is  almost  as  great  as  that 
due  to  the  first,  but  that  the  third  application  gives  a 
smaller,  and  the  fourth  a  still  smaller  increase. 

As  the  nitrogen  increases  the  character  of  the 
development  changes,  the  extra  growth  is  seen  more  in 
the  straw — z>.,  in  the  vegetative  parts  of  the  plant — than 
in  the  grain ;  the  fourth  addition  of  43  lb.  nitrogen  only 
increases  the  yield  of  grain  by  half  a  bushel,  but  the 
straw  is  greater  by  3-9  cvvts.  The  proportion  which  the 
grain  bears  to  the  straw — 62  per  cent,  when  no  nitrogen 
is  used — drops  with  each  increment  of  nitrogen,  and  falls 
to  48  per  cent,  when  172  lb.  of  nitrogen  per  acre  are 
applied.  An  excess  of  nitrogen  also  tells  upon  the 
quality  of  the  grain,  as  judged  by  the  size  of  the  berry 
and  the  weight  per  bushel.  The  weight  per  bushel 
increases  for  the  first  application  of  nitrogen,  but  after 
that  it  becomes  less  and  less  with  each  increment; 
other  results  from  the  same  field  show  a  parallel  varia- 
tion for  the  weight  of  a  hundred  grains  and  for  the 
average  market  value  of  the  corn  from  the  different 
plots. 

When  dealing  with  barley,  an  exactly  similar  state 
of  things  prevails :  the  proportion  the  grain  bears  to 
the  straw  decreases  with  each  addition  of  nitrogen ; 
while  as  regards  the  quality  of  the  grain,  the  weight  per 
bushel  falls,  the  percentage  of  nitrogen  increases,  and 
the  barley  takes  on  all  the  appearances  that  are  summed 
up  as  "  coarse."  This  is  due  to  the  fact  that  the  glume 
and  pale,  vegetative  parts,  are  pushed  on  out  of  propor- 
tion to  the  endosperm,  so  that  the  berry  is  light  and 
appears  thick-skinned ;  at  the  same  time  the  colouring 
matter  is  increased,  though  this  is  more  apparent  in  the 
ear  than  in  the  grain. 


82 


NITROGENOUS  MANURES 


[chap. 


These  differences  may  be  illustrated  by  one  of  the 
Rothamsted  experiments  in  1905,  where  barley  was 
grown  on  one  plot  with  283  lb.  of  nitrogen  in  the  form 
of  wool  dust,  on  the  neighbouring  plot  with  the  residue 
of  the  same  amount  of  shoddy  that  had  been  applied 
the  year  before  to  a  Swede  crop,  and  on  a  third  plot 
with  no  nitrogen.    The  results  are  shown  in  Table  XXI. 

Table  XXL— Effect  of  Excessive  Nitrogen  on  Barley. 
Rothamsted,  1905. 


Weight 

per 
Bushel. 

Grain 

to 

100  Straw. 

Offal  Com 

to  100 

Dressed  Grain. 

Nitrogen. 

No  nitrogen . 

Shoddy,  previous  year  . 

Shoddy,  same  year 

Lb. 

58-0 
57-3 
55-1 

1 10-4 
96-6 
72.8 

5-9 
12.5 

34-9 

Per  cent. 

1. 61 

1.79 
2-42 

This  is  an  extreme  case,  but  it  illustrates  the  effect 
of  an  excess  of  nitrogen  in  producing  a  disproportionate 
amount  of  straw  and  a  thin,  light,  nitrogenous  barley. 
Of  course  some  nitrogen  is  necessary  in  order  to  obtain 
a  good-sized  berry ;  the  long  series  of  Rothamsted 
experiments  all  show  that  high  quality  cannot  be 
secured  by  merely  growing  barley  on  land  exhausted 
of  nitrogen :  it  is  the  excess,  especially  the  relative 
excess  when  the  mineral  constituents  are  deficient, 
that  leads  to  inferior  grain. 

Although  these  results  show  that  the  quality,  and 
therefore  the  composition,  of  the  grain  is  affected  by  the 
amount  of  nitrogen  supplied  to  the  crop,  it  is  really 
astonishing  to  find  how  small  are  the  changes  brought 
about  by  extreme  differences  in  the  manuring. 

To  begin  with,  the  plant  reacts  against  variations  in 
the  composition  of  the  soil  and  tends  to  keep  its  own 
composition  constant ;  when  also  the  time  comes  for  the 


III.] 


EFFECT  OF  SEASON  AND  MANURING 


83 


grain  to  be  formed  from  the  reserve  materials  already 
stored  up  in  the  plant,  another  attempt  is  made  to  turn 
out  a  standard  product. 

Even  on  the  Rothamsted  plots,  where  the  differences 
in  the  supply  of  nutrients  are  extreme  and  have  been 
accumulating  for  fifty  years,  the  composition  of  the 
grain  changes  more  from  one  season  to  another  than 
it  does  in  passing  from  plot  to  plot.  Table  XX 1 1,,  for 
example,  shows  the  percentage  of  nitrogen  in  the 
wheat  grain  and  straw,  from  several  plots  differing  in 
their  nitrogen  supply  in  two  sharply  contrasting 
seasons. 

Table   XXII.— Composition  of    Wheat   Grain   and    Straw   as 

AFFECTED      BY      MANURING     AND      SEASON,      BROADBALK      FiELD, 

Rothamsted  (1852  and  1863). 


2 

3 

7 

10 

11 

Dung. 

-a 

a 

N. 

P.,Og 
K2O. 

N. 
only. 

N. 

P0O5. 

Weight  per  bushel,  lb.      ■  [f^^-^ 
Weight  of  100  grains,  gms.-^      „§ 
Grain  to  100  Straw  .         .  i  \^^^ 
Nitrogen  in  Dry  Grain,  %  -j     g§ 
Nitrogen  in  Dry  Straw,  %  |  ^g^^ 

58-2 
63.1 

3-46 

5-35 

49.6 
67-5 

2 -02 

1-52 

0-46 
0-25 

56-6 
62.7 

2-88 
5 -02 

53-9 

70-4 

2 -08 
1-65 

0-57 
0-33 

:6.o 
62.6 

3'08 
4-79 

41-9 
59-4 

2'29 

1-53 

0-87 
0.36 

55-9 
62-6 

3-26 

4-Si 

47-3 

74-3 

2-48 
1.70 

0-89 

0-35 

55-6 
62.5 

2-94 
4-76 

47-8 

70-4 

1-95 
1-79 

0-46 
0-44 

Of  course  very  great  differences  in  "  quality  "  may 
be  entirely  passed  over  in  a  crude  chemical  analysis 
which  merely  determines  the  amount  of  such  ultimate 
constituents  as  nitrogen,  phosphoric  acid,  etc.  For 
example,  high  nitrogen  content  is  generally  associated 


NITROGENOUS  MANURES 


[chap 


with  good  quality  in  wheat ;  yet  the  flour  made  from 
the  grain  of  the  plots  on  the  Broadbalk  field,  which 
received  the  highest  amount  of  nitrogen,  gives  rise  to 
such  a  loose,  unstable  dough  that  it  can  hardly  be 
formed  into  anything  resembling  a  loaf. 

Table  XXI 1 1,  shows  the  percentages  of  nitrogen  in 
the  grain  and  in  the  flour  made  from  the  grain  grown 
in  1903  on  certain  of  the  Rothamsted  plots,  which  vary 
greatly  as  regards  their  nitrogen  supply. 

Table  XXIII.— Nitrogen  in  Wheat  Grain  and  Flour. 
Broadbalk,  Rothamsted,  1903. 


Plot. 

Manuring. 

Nitrogea 

applied 

per  Acre. 

Nitrogen 
in  Grain. 

Nitrogen 
in  Flour. 

3 
6 

7 
8 

10 
2 

Unmanured . 
Complete  Manure 

))             ))       •         • 

Nitrogen  only 
Farmyard  Manure 

Lb. 
0 

43 

86 
129 

86 
200  (?) 

Per  cent. 
1-844 
1.923 

2-195 
2-332 
2-II3 

2.462 

Per  cent. 
1-462 
1-575 
1-738 
1-785 
1-736 
2-0x4 

The  variations  in  the  nitrogen  content  of  the  flour 
are  extreme,  ranging  from  1-462  for  the  unmanured 
plot  to  2-014  for  the  dunged  plot.  The  increased 
nitrogen  thus  obtained  did  not,  however,  result  in  the 
stronger  flour  which  is  associated  with  a  higher  nitrogen 
content  when  wheat  is  grown  under  more  normal 
conditions,  the  loaves  made  from  the  grain  of  Plots  2  to 
10  being  very  greatly  inferior  to  that  made  from  the 
grain  of  the  unmanured  plot.  This  only  shows  that 
such  a  characteristic  as  the  strength  of  wheat — the 
quality,  as  the  practical  man  would  term  it — is  as  a  rule 
due  to  some  more  subtle  combinations  than  are  measured 
in  ordinary  analysis.  In  this  case  strength  is  not  to  be 
measured  by  the  nitrogen  content,  though  the  two 
often  vary  together. 


III.]  NITROGENOUS  MANURES  AND  COMPOSITION  85 

When  dealing  with  root  crops  like  Swedes  and 
mangolds,  the  effect  of  large  quantities  of  nitrogen 
may  be  seen  to  some  extent  in  an  increased  production 
of  leaf  in  relation  to  the  root,  especially  in  the  case  of 
Swedes,  but  the  variation  thus  induced  is  not  great. 
The  root  or  bulb  is  to  be  regarded  as  a  vegetative 
part  of  the  plant  just  as  much  as  the  leaf;  the  true 
physiological  maturity  does  not  set  in  until  the  second 
season,  when  the  production  of  the  seed  takes  place. 
The  Rothamsted  mangold  plots  afford  a  good  illustra- 
tion, and  Table  XXIV.  shows  the  production  of  root 
and  leaf  and  the  relation  betv/een  them  for  several 
plots  which  vary  in  the  amount  of  nitrogen  supplied, 
in  1900,  a  year  when  a  very  uniform  plant  was  obtained. 

Table  XXIV. — Effect  of  increasing  Nitrogen  Supply  on 
Ratio  of  Root  to  Leaf.    Rothamsted. 


Plot. 

Nitrogen 
supplied, 

lb. 
per  acre. 

Mangolds,  1900. 

Swedes,  1908. 

Root. 

Tons. 

Leaf. 
Tons. 

Root 
Leaf 

Root. 
Tons. 

Leaf. 
Tons. 

Root 
Leaf 

40 

4A 
4AC 

0 

86 

184 

8-75 
28-95 
43-20 

I-IO 

3-25 
6-30 

8-0 
8-9 
6-9 

4-07 
1 1 -48 
11.65 

I'SI 

5-63 

10.94 

2-7 

2-0 
I'l 

The  proportion  of  leaf  is  a  little  greater  with  the 
excessive  dressings  of  nitrogen  applied  to  the  last  two 
plots,  but  ^he  variations  are  not  great  nor  closely 
parallel  to  the  supply  of  nitrogen.  When  Swede  turnips 
were  sown  on  the  same  plots  in  1908  the  increase  of 
leaf  with  the  greater  nitrogen  supply  was  much  more 
manifest,  as  is  shown  in  the  last  three  columns  of  the 
table. 

The  effect  of  the  large  amounts  of  nitrogen  upon 
the  vegetative  development  of  the  plant  is  more  dis- 


86 


NITROGENOUS  MANURES 


[chap. 


tinctly  seen  in  a  prolongation  of  growth  far  into  the 
autumn ;  on  the  plots  receiving  little  or  no  nitrogen 
the  leaves  turn  yellow  and  begin  to  fall  in  early  October, 
when  the  mangolds  on  the  high  nitrogen  plots  are  still 
putting  out  fresh  growths  of  green  leaves  and  showing 
no  signs  of  entering  into  a  resting  period.  It  is  hardly 
possible  to  illustrate  this  effect  by  figures,  but  analysis 
of  the  mangolds  from  these  plots  demonstrate  the 
preponderance  in  the  roots  grown  with  excess  of 
nitrogen  of  such  unelaborated  materials  as  the  nitrates, 
amides,  and  reducing  sugars,  associated  also  with  a 
higher  proportion  of  water. 

Table  XXV. — Composition  of  Barn  Field  Mangolds,  1902. 


Plot. 

S  <"  2 
8)Sg 

§  §3 

60 
0  bJO 

■a  d 

Glucose 
xlOO. 
-f-Cane 
Sugar. 

Nitrogen.                 1 

1 

Total. 

As 
Amide. 

As 

Nitrate. 

40 
4A 
20 

2A 

4AC 

4C, 

Aug. 

28/03 

Lb. 
0 

86 
200 
286 
184 

I98 

15-62 
12-98 
1373 

12-47 
12-78 

11.74 

io-8o 
8-49 
8-86 
7-78 
8-11 

7-II 

0-20 
0-32 
0-30 
0-19 
0-19 

o-i6 

1-85 
3-77 
3-39 
2-44 

2-34 
2-25 

O-II92 
0-1336 
0-1388 
0-1902 
O-1615 

0-1507 

0-0263 
0-0320 
0-0427 
0-0651 
0-0514 

0-0331 

0-0020 
0-0023 
0-0158 
0-0148 
0-0153 

0.0155 

In  November  the  roots  grown  with  excess  of 
nitrogen  approximate  in  composition  to  normally 
manured  roots  taken  in  August,  when  still  growing 
vigorously. 

One  of  the  most  important  effects  upon  plants  of 
an  excess  of  nitrogen  is  their  increased  susceptibility 
to  fungoid  attacks  of  all  kinds;  for  example,  rust  is 
always  much  more  abundant  upon  wheat  which  has 
been  heavily  manured  with  nitrogen,  just  as  it  appears 


III.]        EXCESS  OF  NITROGEN  AND  DISEASE  87 

on  normally  manured  wheat  whenever  the  character 
of  the  season  has  been  such  as  to  induce  a  specially 
rapid  production  of  nitrates  while  the  plant  was  making 
its  growth,  as  when  great  heat  and  moisture  come 
together  in  May.  In  seasons  when  rust  is  prevalent 
the  high  nitrogen  plots  at  Rothamsted  are  always 
markedly  the  more  rusty,  and  can  easily  be  picked  out 
by  their  colour;  the  grass  plots  are  also  marked  by 
their  special  rusts ;  and,  again,  such  a  characteristic 
grass  fungus  as  Epichiloe  typhijia  is  generally  common 
enough  on  the  high  nitrogen  plots  but  absent  from  the 
others.  But  susceptibility  to  disease  brought  about 
by  an  excess  of  nitrogen  is  perhaps  most  strikingly  seen 
at  Rothamsted  on  the  mangold  plots,  though  the  man- 
gold is  a  plant  which,  as  a  rule,  suffers  but  little  from 
fungoid  attacks.  In  September,  however,  the  leaves  of 
the  mangolds  at  Rothamsted  that  receive  an  excess  of 
nitrogen  begin  to  be  attacked  by  a  leaf  spot  fungus, 
Uromyces  betae,  which  develops  rapidly  until  on  the 
worst  plots  all  the  larger  leaves  turn  brown  and  present 
a  burnt-up  appearance,  because  the  spots  of  destroyed 
leaf  tissue  have  become  so  numerous  as  to  run  together. 
Where  the  application  of  nitrogen  has  been  less  heavy 
but  is  still  high,  the  severity  of  the  attack  is  diminished, 
while  the  fungus  is  entirely  absent  from  the  leaves  of 
the  normally  manured  plots,  although  they  are  in  close 
proximity  and  equally  exposed  to  infection.  The 
association  of  high  nitrogenous  manuring  with  suscepti- 
bility to  disease  may  be  seen  in  all  plants ;  it  is  often 
very  manifest  in  greenhouses  where  crops  are  grown 
in  specially  rich  soil,  nitrifying  very  rapidly  owing  to 
the  high  temperature  prevailing.  The  dark  green 
aspect  of  the  leaves  of  such  plants  is  generally  evidence 
of  the  excessive  amounts  of  nitrogen  they  are  receiving, 
and  it  is  well  known  that  if  any  fungoid  disease  makes 


88  NITROGENOUS  MANURES  [chap. 

its  appearance  it  is  very  difficult  to  keep  in  check  and 
often  destroys  the  whole  crop  with  great  rapidity ;  as, 
for  example,  has  been  the  case  with  the  leaf  spot  fungus 
Cercosporium  inelonis,  which  has  of  late  years  proved  so 
destructive  to  cucumbers  grown  under  glass. 

Various  attempts  have  been  made  to  get  a  little 
nearer  to  the  cause  of  this  association  of  high  nitro- 
genous manuring  with  susceptiblity  to  disease.  In  the 
first  place,  certain  physical  differences  can  be  traced 
in  the  tissues  of  the  plants;  just  as  high  nitrogen 
results  in  a  weakness  of  straw  in  cereals,  due  to  a 
long-jointed  soft  stem,  so  the  cuticle  of  the  leaf  and 
the  cell  walls  of  the  leaf  tissue  are  measurably  thinner 
when  the  plant  has  been  grown  with  an  excess  of 
nitrogen.  The  cause  is,  however,  more  probably  to  be 
found  in  some  alteration  in  the  composition  of  the  cell 
sap,  which  renders  it  a  better  medium  for  the  growth 
of  the  fungus  in  question.  It  has  been  found,  for 
example,  that  spores  of  the  Uromyces  betae  will  grow 
freely  upon  a  bruised  surface  of  the  mangold  leaves 
grown  with  excess  of  nitrogen,  but  make  no  headway 
when  sown  upon  a  similarly  bruised  surface  of  the  leaf 
of  a  normally  manured  plant 

The  softness  of  tissue  that  is  induced  by  large 
applications  of  nitrogenous  manure — most  markedly  by 
nitrate  of  soda,  because  of  its  immediate  availability — 
is  recognised  in  other  ways ;  for  example,  cabbages  and 
similar  vegetables  grown  rapidly  with  nitrate  of  soda 
are  preferable  for  immediate  consumption  because  of 
their  tenderness,  but  in  the  market  they  bear  a  bad 
reputation,  because  the  same  softness  of  tissue  leads 
to  rapid  wilting  and  a  faded  appearance  when  the 
vegetables  have  been  cut  for  some  time  and  have 
experienced  the  usual  amount  of  rough  handling  in 
transit. 


III.]  DOMINANT  FERTILISERS  89 

When  various  crops  are  considered  in  relation  to 
manures,  they  are  found  to  show  considerable  differences 
in  their  response  to  the  individual  elements  of  nutrition, 
differences  which  are  only  to  be  ascertained  by  trial, 
but  which  are  not  determined  by  the  greater  or  less 
amount  of  the  fertilising  ingredient  in  question  taken 
up  from  the  soil.  For  example,  Ville  introduced  the 
idea  that  for  each  plant  there  is  a  "  dominant "  element 
of  fertility,  and  if  the  requirements  of  the  plant  in  this 
respect  are  satisfied  it  is  generally  capable  of  obtaining 
the  other  necessary  constituents  from  the  soil.  For 
wheat,  grass,  and  mangolds,  nitrogen  is  the  dominant ; 
under  ordinary  conditions  of  farming  if  the  wheat  crop 
is  well  supplied  with  nitrogen  it  is  waste  of  money 
to  give  it  any  phosphatic  manure  or  potash  salts, 
because  neither  will  result  in  any  adequate  increase 
of  crop,  supposing  the  soil  to  show  no  abnormal 
deficiencies.  Without  pushing  the  idea  too  far,  it  may 
generally  be  recognised  that  when  the  land  is  in  good 
condition  most  of  our  crops  require  a  special,  rather 
than  a  general  manuring;  the  plant,  owing  to  some 
peculiarity  in  its  habit  of  growth,  finds  a  particular 
difficulty  to  obtain  one  of  the  constituents  of  its  nutri- 
ment from  the  soil ;  if  that  weak  spot  is  repaired  by 
the  manure  employed,  the  soil  will  furnish  the  other 
essentials  for  growth.  For  example,  wheat  and  barley, 
cereals  that  are  so  similar  in  their  general  character, 
demand  entirely  distinct  treatment ;  under  ordinary 
farming  conditions,  wheat,  as  we  have  stated  above, 
requires  an  active  nitrogenous  manure  and  little  else; 
barley  requires  comparatively  little  nitrogen,  but  is  very 
responsive  to  a  supply  of  phosphates. 

This  contrast  between  wheat  and  barley  is  due  to 
the  differences  in  the  time  and  growth  of  the  two 
plants :  wheat  is  generally  grown  in  the  autumn  after 


90  NITROGENOUS  MANURES  [chap. 

a  single  ploughing,  and  this  light  preliminary  prepara- 
tion of  the  soil  is  not  followed  up  by  any  further 
cultivation  except  rolling,  and  possibly  a  single  hoeing. 
The  winter  rainfall  not  only  washes  away  much  of  the 
nitrate  that  may  have  been  present  in  the  soil  at  the 
end  of  the  summer,  but  it  also  tends  to  set  the  soil  down 
into  a  close  mass,  in  which  aeration  may  become  defec- 
tive. The  main  growth  of  the  crop  takes  place  also 
during  the  early  spring  months  when  low  temperatures 
prevail ;  and  all  these  causes  work  together  to  reduce 
the  rate  of  decay  and  nitrification,  and  so  keep  the  soil 
poorly  supplied  with  nitrates.  In  consequence,  wheat  is 
specially  responsive  to  an  early  supply  of  some  active 
compound  of  nitrogen,  such  as  nitrate  of  soda  or  sul- 
phate of  ammonia.  But  apart  from  this  difficulty  in 
obtaining  nitrogen,  wheat  possesses  a  very  extensive  root 
system  and  also  has  a  comparatively  prolonged  period 
of  growth,  by  which  means  it  is  able  to  satisfy  its 
requirements  for  potash  and  phosphoric  acid,  even  on 
comparatively  poor  land. 

Barley,  on  the  other  hand,  is  a  comparatively  shallow- 
rooted  crop,  occupying  therefore  a  much  more  restricted 
layer  of  soil,  and  possessing  but  a  short  period  of  growth ; 
it  has  not  the  same  opportunity  as  wheat  to  search  for 
phosphates,  and  thus  becomes  specially  dependent  upon 
an  artificial  supply.  Barley,  further,  makes  its  chief 
growth  at  rather  a  later  date  in  the  spring  than 
wheat  does;  the  land  receives  a  spring  cultivation 
before  the  barley  is  sown  and  the  tilth  is  not  destroyed 
by  the  winter  rains.  Thus  the  nitrification  of  the 
natural  reserves  of  the  soil  can  count  for  much  more 
in  the  nutrition  of  barley,  and  in  consequence  external 
supplies  of  nitrogen  are  rarely  required. 

Swede  turnips  afford  another  example  of  a  crop 
comparatively    indifferent    to    nitrogenous    manuring, 


III.]  NITROGEN  REQUIRED— HABIT  OF  GROWTH    91 

although  large  amounts  of  nitrogen,  100  to  150  lb. 
per  acre,  are  taken  up  from  the  soil.  The  turnip 
is  a  shallow-rooted  crop  possessing  a  considerable 
development  of  small  fibrous  roots,  but  which  are 
confined  to  a  surface  layer  of  restricted  depth ;  as  a 
rule,  the  crop  is  grown  with  a  moderate  dressing  of 
farmyard  manure  and  4  to  5  cwts.  per  acre  of  phosphates. 
When  farmyard  manure  is  not  used,  \  cwt.  per  acre 
of  sulphate  of  ammonia  or  its  equivalent  is  found  to 
be  enough  nitrogenous  manure ;  and  in  the  south  and 
east  of  England  even  that  is  sometimes  omitted  when 
the  land  is  in  good  heart.  But  the  land  receives  a  very 
thorough  preparation  during  the  spring  months  before 
the  seed  is  sown,  so  that  the  fine  seed-bed  has  already 
been  enriched  by  an  accumulation  of  nitrates,  the  pro- 
duction of  which  has  been  greatly  stimulated  by  the 
working  and  aeration  of  the  soil.  The  seed  is  not 
sown  until  the  end  of  May  or  early  June,  by  which 
time  temperatures  are  high  and  nitrification  very 
active,  and  the  growth  of  the  crop  is  accompanied  by 
continual  hoeing  and  working  of  the  land  between 
the  rows.  There  thus  continues  to  be  produced  in  a 
rich  soil  sufficient  nitrates  for  the  requirements  of  the 
crop,  and  large  external  supplies  in  the  manure  are 
unnecessary.  Mangolds,  on  the  contrary,  are  a  much 
deeper  rooted  plant,  are  sown  earlier  and  generally  on 
stronger  soils  less  adapted  to  rapid  nitrification,  and 
are  found  by  experience  to  require  a  far  greater 
supply  of  nitrogenous  manure. 

One  of  the  most  important  questions  to  be  settled 
in  connection  with  nitrogenous  manures  is  their  relative 
availability  and  rapidity  of  action.  It  has  already  been 
stated  that  the  nitrates  are  both  soluble  and  can  be 
taken  up  without  further  change  by  the  plant;  the 
ammonium  salts  as  a  rule  require  to  be  nitrified,  but 


92  NITROGENOUS  MANURES  [chap. 

this  action  is  speedy  in  normal  soils,  whereas  the 
organic  compounds  of  nitrogen  have  to  undergo 
several  successive  processes  of  bacterial  breaking  down 
before  they  reach  the  plant,  so  that  some  of  them,  like 
straw  and  the  residues  of  protein  digestion,  may  remain 
for  a  very  long  period  in  the  soil  before  their  nitrogen 
becomes  converted  into  nitrate. 

It  is  important  for  the  farmer  to  know  what  return 
he  may  expect  from  a  given  nitrogenous  manure  in  the 
year  of  its  application,  and  whether  the  nitrogen  which 
is  not  recovered  by  the  first  crop  may  be  expected  to 
become  available  in  the  next  or  following  seasons.  It 
is  necessary  even  to  put  a  money  value  upon  the 
residues  left  behind  in  the  soil  after  the  first  crop  has 
been  grown  with  the  manure,  because  a  tenant  leaving 
his  farm  is  entitled  to  compensation  for  the  unexhausted 
fertility  he  has  thus  added  to  the  soil  but  has  had  no 
opportunity  of  cropping  out. 

A  large  number  of  investigations  have  been  made 
as  to  the  relative  value  of  nitrogen  combined  as  nitrate 
of  soda  and  sulphate  of  ammonia;  but  it  has  already 
been  explained  in  the  preceding  chapter  that  the 
comparative  effect  of  nitrogen  from  these  two  sources 
will  be  determined  by  a  variety  of  external  conditions, 
such  as  the  crop  under  consideration,  the  amount  of 
calcium  carbonate  in  the  soil,  the  supply  of  potash, 
dormant  or  available,  and  the  effect  of  the  manures 
upon  the  tilth  of  the  soil ;  in  consequence,  no  general 
answer  is  possible  that  will  apply  to  all  cases.  From 
the  Rothamsted  experiments  it  is  found  that  nitrate 
of  soda  affords  the  better  source  of  nitrogen  for  wheat, 
grass,  and  mangolds,  the  superiority  amounting  on  the 
average  to  about  ten  per  cent. ;  but  that,  for  barley, 
potatoes,  and  turnips,  the  two  manures  are  of  equal 
value,  nitrogen  for  nitrogen. 


III.]    AVAILABILITY  OF  NITROGENOUS  MANURES  93 

While  these  results  might  not  be  exactly  borne  out 
on  other  soils,  it  will  be  within  the  limits  of  ordinary 
error  to  conclude  that,  for  equal  amounts  of  nitrogen, 
nitrate  of  soda  possesses  a  slightly  greater  value  than 
sulphate  of  ammonia,  but  that  the  choice  between  the 
two  should  be  dictated  by  the  relative  price  of  the 
nitrogen  per  unit,  the  nature  of  the  crop,  and  the 
amount  of  carbonate  of  lime  in  the  soil.  Since  sulphate 
of  ammonia  contains  approximately  20  per  cent,  of 
nitrogen  against  15  per  cent,  in  nitrate  of  soda,  the 
relative  prices  of  the  two  manures  ought  to  be  in  the 
ratio  of  3  to  4;  if  sulphate  of  ammonia  is  £\2  per 
ton,  nitrate  of  soda,  to  yield  an  equivalent  value  of 
nitrogen,  ought  not  to  cost  more  than  £(^  per  ton ;  if 
nitrate  of  soda  is  £\o  per  ton,  the  equivalent  value  of 
sulphate  of  ammonia  would  be  ;;^I3,  6s.  8d.  per  ton. 
For  mangolds,  nitrate  of  soda  should  certainly  be 
chosen,  unless  the  advantage  in  price  is  largely  on 
the  side  of  the  sulphate  of  ammonia,  because  of  the 
great  value  of  the  soda  base  in  rendering  available 
the  dormant  potash  so  much  required  by  the  mangold. 
On  soils  short  of  lime,  and  especially  if  they  have  any 
tendency  to  become  acid,  nitrate  of  soda  will  always  be 
preferable ;  and  again,  when  extra  large  quantities  of 
nitrogenous  fertilisers  are  to  be  used,  as  is  sometimes 
the  case  in  market-garden  work.  For  barley,  sulphate 
of  ammonia  is  preferable,  because  of  the  better  quality 
it  produces ;  on  the  light  soils  also  it  should  have  the 
preference,  provided  they  are  properly  supplied  with 
carbonate  of  lime. 

But  undoubtedly  the  best  plan  is  to  use  a  mixture 
of  the  two  fertilisers ;  there  is  then  nitrate  for  the 
immediate  use  of  the  crop,  and  yet  no  great  excess  of 
salt  remains,  with  the  risk  of  its  being  washed  down 
below  the  range  of  the  plant's  roots  in  the  soil  water ; 


04 


NITROGENOUS  MANURES 


[chap. 


the  nitrification  of  the  ammonia  continues  the  supply 
of  nitrate  at  a  later  stage,  and  the  injurious  effects 
upon  the  soil  of  the  two  manures,  nitrate  of  soda  as 
a  producer  of  alkali,  and  sulphate  of  ammonia  as  causing 
acidity,  neutralise  one  another. 

Several  of  the  organic  compounds  of  nitrogen,  such 
as  those  contained  in  Peruvian  guano,  rape  cake,  and 
dried  blood,  are  almost  as  active  sources  of  nitrogen  as 
the  salts  of  ammonia,  especially  when  used  continuously, 
so  that  the  residues  left  in  any  one  year  are  available 
for  succeeding  crops.  For  example,  the  Rothamsted 
barley  plots  receive  equal  weights  of  nitrogen  as 
nitrate  of  soda,  sulphate  of  ammonia,  and  rape  cake ; 
and  as  the  following  table  shows,  the  returns  from  the 
rape  cake  are  but  little  below  those  from  the  other  two 
manures. 

Table  XXVI.— Nitrogenous  Manures  with  Minerals. 
Average  Yield  of  Barley  (1852-1901).    Rothamsted. 


Plot. 

Manuring. 

Grain. 

Straw. 

4A 

4N 
4C 

Ammonium  Salts  =  43  lb.  N.  . 
Nitrate  of  Soda  -  43  lb.  N.     . 
Rape  Cake  =  49  lb.  N.    . 

Bushels. 
42.1 
43-6 
41-0 

Cwts. 

25-0 

27-4 
24.5 

These  results  do  not,  however,  show  how  much 
return  from  the  given  manure  is  obtained  in  the  year 
of  application,  but  from  other  of  the  Rothamsted  plots 
we  learn  that  on  such  a  soil  neither  nitrate  of  soda  nor 
ammonium  salts  leave  any  appreciable  residue  behind. 
On  the  wheat  field,  two  of  the  plots  receive  in  alternate 
years  either  400  lb.  of  ammonium  salts  or  a  mixture  of 
complete  mineral  manures  ;  so  that  in  any  year  there  is 
one  plot  with  the  ammonium  salts  and  the  residue  of 
the  previous  year's  minerals,  and  another  with  mineral 


III.]  RESIDUES  LEFT  BY  NITROGENOUS  MANURES  gj 

manures  and  a  residue  of  ammonium  salts.  The  results 
are  set  out  in  Table  XXVII.,  the  basis  of  comparison 
being  a  third  plot,  which  receives  both  the  ammonium 
salts  and  the  mineral  salts  in  the  same  year,  and  a 
fourth  plot,  which  never  receives  any  ammonium  salts, 
but  the  minerals  every  year. 

Table  XXVII.— Residual  Effect  of  Manures. 

ROTHAMSTED.      WHEAT  (1852-I902). 


Plot. 

Manuring. 

Grain. 

Straw. 

Bushels. 

Cwts. 

7 

400   lb.   Ammonium    Salts    and 

Minerals.         .... 

32-9 

33-0 

17 

400   lb.    Ammonium   Salts    and 

Mineral  Residues   . 

30-4 

29-5 

18 

Minerals  +  Residues  of  400   lb. 

Ammonium  Salts    . 

15-3 

I3-I 

5 

Minerals  only      .... 

14-9 

12-2 

Thus  the  residue  from  the  ammonium  salts  applied 
in  the  previous  year  only  raises  the  yield  by  0-4  bushel 
of  grain  and  0-9  cwt.  of  straw  above  the  yield  of  the 
plot  which  never  receives  any  nitrogen,  whereas  the 
application  of  fresh  ammonium  salts  on  Plot  7  causes 
an  increase  of  18  bushels  of  grain  and  20-8  cwt.  of 
straw.  On  the  other  hand  Plot  17,  with  the  residues  of 
mineral  manures  applied  in  the  previous  year,  only  falls 
behind  Plot  7  to  which  they  had  been  applied  in  the 
same  year,  by  2-5  bushels  of  grain,  and  3-5  cwt.  of  straw. 

A  very  similar  experiment  is  included  among  the 
Woburn  plots,  the  only  difference  being  that  there  the 
minerals  are  put  on  every  year,  and  that  the  trials  are 
also  repeated  with  nitrate  of  soda. 

Table  XXVIII.  shows  the  average  results  for  the 
five  years,  1882-86,  from  which  it  will  be  seen  that  the 
ammonium  salts  left  behind  considerable  residues  which 


96 


NITROGENOUS  MANURES 


[chap. 


were  of  service  to  the  succeeding  crop,  while  little 
benefit  was  derived  from  the  preceding  year's  application 
of  nitrate  of  soda.  With  barley  the  residues  from  both 
manures  were  more  pronounced. 

Table  XXVIII.— Effect   of   Nitrate  of   Soda  and  Ammonium 
Salts  applied  in  the  Previous  Year.    Woburn  (1882-1886). 


Plot. 


4 
ia 

93 


Maunring. 


Wheat. 


Minerals  only  . 

Minerals  +  Residue     of    Ammonium 

Salts     ...... 

Minerals  +  Ammonium  Salts     . 
Minerals  +  Residue     of    Nitrate    of 

Soda 

Minerals  +  Nitrate  of  Soda 


Bushels. 
18.3 

20-4 

42.8 
I7.I 

40-9 


Barley. 


Bushels. 
24-6 

37-0 
55-5 

34-5 
59-9 


This  essential  difference  in  the  results  at  Rotham- 
sted  and  Woburn  arises  from  two  causes ;  in  the  first 
place,  the  soil  at  Woburn  is  very  deficient  in  carbonate 
of  lime,  indeed  at  a  later  date  than  the  period  from 
which  the  figures  in  the  table  are  quoted  the  soil  of  the 
barley  plots  had  become  so  acid  that  the  crop  would  no 
longer  grow.  Under  these  conditions  nitrification  will 
be  very  slow  and  some  of  the  ammonium  salts  will  be 
retained  unchanged  in  the  soil  until  the  following  season, 
instead  of  nitrifying  and  so  getting  into  a  form  that 
will  wash  through  the  soil.  Thus  the  ammonium  salts 
will  leave  a  much  greater  residue  than  the  nitrate ; 
that  the  latter  has  any  effect  in  the  following  season 
must  be  set  down  to  the  texture  of  the  fine  sandy 
loam  at  Woburn,  which  admits  of  a  much  greater  capil- 
lary rise  of  the  soil  water  than  is  possible  in  the  close 
Rothamsted  soil,  with  the  result  that  some  of  the 
nitrates  which  have  been  washed  down  during  the 
winter  are  brought  back  to  the  surface. 


III.]  AVAILABILITY  OF  NITROGENOUS  MANURES  97 

In  the  main,  however,  it  will  be  safer  to  regard  the 
fertilising  effect  of  both  sulphate  of  ammonia  and  nitrate 
of  soda  as  confined  to  the  season  of  their  application ; 
the  only  residues  they  leave  behind  being  due  to  the 
increased  root  and  stubble  left  in  the  land  and  the 
extra  nitrogen  in  the  crop,  some  of  which,  e.g.,  the 
nitrogen  in  the  straw  or  the  roots  grown,  does  remain 
on  the  farm  as  a  permanent  addition  to  the  stock  of 
fertility. 

Wagner  of  Darmstadt  has  made  a  very  extensive 
series  of  comparisons  of  various  nitrogenous  manures 
based  upon  experiments  in  pots,  and  from  them  has 
compiled  the  following  table,  showing  the  comparative 
recovery  in  the  crop  of  100  of  nitrogen  supplied  in  each 
fertiliser. 


Table  XXIX. — Return  in  Crop  for  100  Nitrogen  applied  and 
Relative  Value  when  Nitrate  of  Soda  =  100.    Wagner. 


Nitrate  of  Soda          ,        . 

82 

100 

Ammonium  Salts 

77 

94 

Peruvian  Guano        , 

71 

87 

Green  Plants     . 

63 

77 

Horn  Meal        ,        , 

61 

74 

Dried  Blood     . 

60 

73 

Castor  Cake      . 

60 

73 

Wool  Dust 

21 

26 

Cow  Dung        « 

18 

22 

Leather  Meal    . 

13 

16 

These  results  are,  however,  based  upon  the  results  of 
pot  experiments,  which,  because  of  the  rapid  variations 
of  temperature  and  the  comparative  concentration  of 
manures  employed,  are  always  somewhat  unfair  to 
organic  manures,  especially  to  the  bulky  ones  coming 
at  the  lower  end  of  the  scale. 

Experiments  have  been  carried  out  of  late  years  at 
Rothamsted  to  examine  the  question  from  a  slightly 
different  point  of  view  by  means   of  field  plots.     The 

G 


98 


NITROGENOUS  MANURES 


[chap. 


scheme  of  experiment  is  to  take  four  plots  for  each 
manure  ;  one  receives  the  manure  in  any  particular  year, 
while  the  others  remain  unmanured  except  for  the 
residues  that  may  remain  from  a  similar  application 
that  had  been  made  one,  two,  and  three  years  pre- 
viously, a  fifth  plot  continuously  unmanured  being 
employed  as  a  check. 

The  experiments  have  not  been  in  progress  long 
enough  to  enable  exact  results  to  be  obtained,  especially 
as  regards  the  residues  remaining  in  the  second  or 
third  year  after  the  application,  but  the  following 
figures  show  the  kind  of  return  which  may  be  antici- 
pated. In  order  to  eliminate  the  effect  of  season  and 
crop,  the  increase  given  by  a  residue  is  always  compared 
with  the  increase  brought  about  by  a  fresh  application  of 
the  same  manure,  which  increase  is  reckoned  as  lOO. 

Table  XXX.— Increased  Yield  due  to  residues  of  Nitrogenous 
Manures  compared  with  Increase  produced  in  First  Year. 
Rothamsted. 


Year  of 
Application. 

Second  Year. 

Third  Year. 

Dung          .         .         . 
Wool  Waste 
Peruvian  Guano         . 
Rape  Cake 

lOO 
TOO 
100 

loo 

46 

79 
12 

9 

37 
38 

12 

2 

Thus  rape  cake,  a  manure  which  we  have  seen  to 
be  comparatively  active,  leaves  behind  for  the  following 
year  a  very  small  residue,  having  only  9  per  cent,  of 
the  effect  of  a  fresh  application  of  manure ;  whereas  a 
wool  shoddy  increases  the  crop  in  the  second  year  by  as 
much  as  79  per  cent,  of  the  increase  produced  by  a  fresh 
application  of  the  same  manure,  and  even  after  two 
crops  have  been  removed  the  residue  is  still  one-third 
as  effective  as  a  fresh  application. 


III.]  RECO  VER  V  OF  NITROGEN  IN  CROP  99 

From  many  of  the  Rothamsted  experiments  it  is 
possible  to  calculate  how  much  of  the  manure  applied 
year  after  year  has  been  eventually  recovered  in  the 
crop ;  with  the  mangold  crop  it  will  be  shown  later  that 
(Table  LXIII.)  78  per  cent,  of  the  nitrogen  applied  as 
nitrate  of  soda  was  recovered  in  the  crop,  the  percentage 
falling  to  71  for  rape  cake,  57  for  ammonium  salts,  and 
only  31  per  cent,  for  dung.  When  manures  were 
applied  to  plots  which  were  also  enriched  with  dung  the 
recovery  was  less  in  all  cases,  the  usual  law  of  diminish- 
ing.returns  coming  into  play. 

It  cannot  be  said  that  the  conclusions  which  may  be 
drawn  from  these  results  as  to  the  relative  availability 
of  different  compounds  of  nitrogen  are  in  any  way 
endorsed  by  their  price  in  the  market,  or  by  the  general 
opinions  of  farmers.  From  the  experimental  point  of 
view  the  value  of  the  different  compounds  of  nitrogen, 
unit  for  unit,  ought  to  be  proportional  to  their  avail- 
ability ;  a  slow-acting  manure  not  only  involves  a  delay 
in  realising  the  capital  that  has  been  put  into  the  land, 
but  much  of  the  residue  is  never  recovered  at  all.  Not- 
withstanding this  the  farmer  has  a  strong  preference,  to 
which  credit  must  be  given  as  founded  upon  experience, 
for  the  organic  sources  of  nitrogen  ;  furthermore,  prices 
fluctuate  in  accordance  with  accidents  of  supply  that 
are  quite  independent  of  agriculture.  For  example, 
the  relative  value  of  nitrogen  in  nitrate  of  soda  and 
sulphate  of  ammonia,  which  may  be  regarded  as 
equally  valuable  in  farming  opinion,  has  fluctuated 
widely  of  late  years ;  on  occasion  the  nitrogen  in 
sulphate  of  ammonia  has  been  the  dearer  of  the  two, 
while  at  other  times  it  has  been  so  much  the  cheaper 
that  the  price  per  ton  of  sulphate  of  ammonia,  with 
20-21  per  cent,  of  nitrogen,  has  fallen  below  that  of 
nitrate  of  soda  with  15-16  per  cent,  of  nitrogen.     The 


lOO  NITROGENOUS  MANURES  [CHAt. 

unit  of  nitrogen  in  dried  blood  is  always  expensive, 
because  of  the  limited  supply  of  this  material  and  the 
special  value  to  manure  manufacturers  it  possesses  for 
compounding  purposes ;  in  rape  cake,  nitrogen  is  also 
greatly  above  the  average  price,  because  of  the  compara- 
tively short  supply  of  this  manure.  Again,  in  Peruvian 
guano  the  unit  of  nitrogen  always  costs  more  than  in 
the  average  run  of  manures,  whereas  in  fish  and  meat 
guanos  it  ranges  at  almost  the  same  price  as  in  sulphate 
of  ammonia.  Finally,  in  all  the  shoddies  and  waste 
materials  of  that  nature  the  price  of  the  unit  of  nitrogen 
is  extremely  variable,  a  large  proportion  being  made  up 
by  the  cost  of  carriage  of  so  bulky  a  material,  but,  as  a 
rule,  it  will  not  be  more  than  one-half  of  the  price  asked 
for  nitrogen  in  its  more  available  forms.  At  the  time  of 
writing,  the  unit  of  nitrogen  in  Peruvian  guanos  costs 
about  1 8s.  and  rather  more  in  dried  blood  and  rape  dust, 
in  fish  guano  about  17s.,  in  nitrate  of  soda  about  i6s., 
in  meat  guano  about  14s.,  and  in  sulphate  of  ammonia 
about  13s.,  while  shoddies  can  be  obtained  in  which  it 
costs  as  little  as  6s. 

Putting  aside  shoddy,  it  is  thus  seen  that  the 
farmer  is  prepared  to  pay  more  for  nitrogen  in  any 
form  of  organic  combination  than  in  its  inorganic  salts, 
though  all  the  experimental  evidence  goes  to  show  that 
the  latter  give  the  larger  and  speedier  returns  in  the 
crop. 

What,  then,  is  the  origin  of  this  strong  prejudice 
of  the  farmer  in  favour  of  an  organic  source  of  nitrogen, 
the  prejudice  which  is  further  seen  in  the  common 
description  of  nitrate  of  soda  and  sulphate  of  ammonia 
as  stimulants  or  even  "  scourges  "  of  the  soil,  rather  than 
plant  foods  ?  Of  course,  no  purely  nitrogenous  sub- 
stance is  a  complete  manure  ;  cropping  with  one  alone 
must  eventually  exhaust  the  land  of  phosphoric  acid  or 


III.]  VALUE  OF  ORGANIC  MANURES  loi 

potash ;  but,  as  has  already  been  shown,  the  reserves  of 
such  materials  in  the  soil  are  so  large  that  long- 
continued  cropping  would  be  needed  to  deplete  them 
seriously. 

Some  other  source  must  be  found  for  the  farmer's 
prejudice,  and  its  true  cause  is  probably  the  manner  in 
which  organic  manures  improve  the  tilth  of  the  soil  by 
maintaining  the  stock  of  humus,  whereas  sulphate  of 
ammonia,  and  particularly  nitrate  of  soda,  injure  it. 
The  importance  of  this  factor  of  tilth  will  be  more 
realised  when  we  remember  that  nearly  the  whole  of  the 
farmer's  labour  in  spring  is  directed  towards  obtaining 
a  fine  seed-bed  for  such  crops  as  barley  and  roots. 
Furthermore,  if  the  weather  conditions  are  adverse  to 
the  start  of  the  crop,  the  eventual  yield  will  depend 
more  upon  the  condition  of  the  seed-bed  than  upon  any 
other  factor. 

The  potent  effect  of  organic  manures  in  promoting 
a  good  tilth  is  very  clearly  shown  by  the  Rothamsted 
experiments  upon  mangolds,  where  the  nitrogenous 
manures  are  nitrate  of  soda,  sulphate  of  ammonia,  and 
rape  cake  respectively.  In  a  good  season  the  nitrate  of 
soda  is  the  most  effective  manure ;  but  taking  an  average 
over  the  whole  period,  rape  cake  shows  a  great  superi- 
ority, simply  because  of  the  difficulty  of  jetting  a  full 
plant  upon  the  other  plots.  Though  all  the  plots  are 
cultivated  in  the  same  way  and  at  the  same  time,  the 
condition  of  the  soil  has  become  so  bad  where  purely 
inorganic  manures  have  been  used,  that  only  in  favour- 
able seasons  is  what  a  farmer  would  call  a  good  plant 
obtained  on  the  nitrate  and  the  ammonia  plots,  whereas 
the  rape  cake  plot  starts  regularly  enough.  On  three 
occasions  the  plant  has  completely  failed  on  the 
ammonia  and  nitrate  plots.  Even  in  the  other  years 
there  are  great  deficiencies,  as  shown  by  the  average 


I02 


NITROGENOUS  MANURES  [chap.  in. 


number  of  plants  counted  on  each  plot,  which  is  set  out 
in  Table  XXXI. 

Table  XXXI.— Effect  of  Manures  upon  the  Number  of  Roots. 

ROTHAMSTED   MANGOLDS,    1876-1902. 


Plot. 


4C 
4A 

4N 


Manures 


Complete  Minerals  with  Rape 
Cake 

Complete  Minerals  with  Am- 
monium Salts     . 

Complete  Minerals  with  Ni- 
trate of  Soda 


Average  Crop 
per  acre. 


Tons. 
21-3 
14.9 
1 8-0 


Average  Number 
of  Boots 
per  acre. 


Number. 

17,474 
14,802 
14.130 


In  ordinary  farming  the  effect  upon  the  soil  is  never 
likely  to  become  so  pronounced  as  in  these  experiments 
at  Rothamsted,  but  without  a  doubt  a  considerable 
element  in  the  extra  value  which  the  farmer  sets  on 
organic  nitrogen  must  be  put  down  to  its  improvement 
of  the  texture  of  the  soil,  a  factor  the  farmer  rightly 
regards  as  of  the  first  importance. 


CHAPTER   IV 

PHOSPHATIC   MANURES 

TheThosphates  of  Calcium — The  Early  Use  of  Bones  as  Manure — 
Preparation  of  Bone  Meal  and  Steamed  Bone  Flour — Dis- 
solved Bones  and  Bone  Compounds — The  Discovery  of 
Mineral  Phosphates,  Coprolites,  Phosphorite,  Phosphatic 
Guanos,  Rock  Phosphates — The  Invention  of  Superphosphate, 
Lawes  and  Liebig — The  Manufacture  of  Superphosphate — 
The  Manufacture  of  Basic  Slag — Nature  of  the  Phosphoric 
Acid  Compounds  in  Basic  Slag  :  their  Solubility  in  Dilute 
Acid  Solutions — Basic  Superphosphate — Wiborg  Phosphate — 
Wolter  Phosphate. 

Although  the  fertilising  effect  of  bones,  in  common 
with  most  other  substances  of  animal  origin,  had  been 
known  in  an  empirical  way  for  a  very  long  time,  the 
efficacy  was  generally  put  down  to  the  oil  they  con- 
tained, and  it  was  only  at  the  close  of  the  eighteenth 
century  that  attention  became  fixed  on  the  phosphoric 
acid. 

Lord  Dundonald,  in  his  Treatise  on  the  Connection  of 
Agriculture  with  Chemistry,  published  in  1795,  had 
arrived  at  a  very  sound  perception  of  the  case.  When 
treating  of  phosphate  of  lime,  he  writes  that  it  "is 
contained  in  animal  matters,  such  as  bone,  urine,  shells, 
etc.,  in  some  sorts  of  limestone,  and  in  vegetable  sub- 
stances, particularly  in  the  gluten,  or  the  vegeto-animal 
part  of  wheat  and  other  grain.  It  is  a  saline  compound, 
very   insoluble.      There   is   reason   to    believe   a   very 


104  PHOSPHATIC  MANURES  [chap. 

considerable  proportion  of  this  nearly  insoluble  salt  is 
contained  in  most  fertile  soils.  .  .  .  These  alkaline 
phosphates  (potash  and  soda)  will  be  found  to  promote 
vegetation  in  a  very  great  degree,  the  substance  of 
which  they  are  composed,  viz.,  alkaline  salts  and 
phosphoric  acid,  are  found  in  the  ashes  of  most 
vegetables."  Again,  Kirwan  writes  in  1796  about  the 
constituents  of  plants :  "  Phosphorated  calx  is  found  in 
greatest  quantity  in  wheat,  where  it  contributes  to  the 
formation  of  animal  gluten.  .  .  .  Hence  the  excellence 
of  bone  ashes  as  a  manure  for  wheat.  .  .  ."  Finally, 
de  Saussure,  in  his  Recherches  Chimiques  sur  la  Vegeta- 
tion, published  in  1804,  writes  :  "  Le  phosphate  de  chaux 
contenu  dans  un  animal,  ne  fait  peut-etre  pas  la  cinq 
centieme  partie  de  son  poids :  personne  ne  doute 
cependent  qu  ce  sel  ne  soit  essential  a  la  constitution 
de  ses  os.  J'ai  trouve  ce  meme  sel  dans  les  cendres  de 
tous  les  v^getaux  ou  je  I'ai  recherche,  et  nous  n'avons 
aucune  raison  pour  affirmer  qu'ils  puissent  exister  sans 
lui."  This  opinion  was  repeated  by  Davy,  and  adopted 
and  disseminated  by  Liebig,  by  which  time  various 
other  experimenters  had  reached  the  conclusion  that 
the  mineral  and  not  the  organic  matter  contained  in 
bones  was  their  chief  fertilising  constituent. 

Since  all  the  phosphatic  manures  which  possess  any 
practical  importance  are  phosphates  of  calcium,  it  is 
necessary  to  discuss  these  compounds  a  little  before 
proceeding  further.  The  phosphatic  material  which  is 
most  widely  disseminated,  occurring  in  all  the  primitive 
crystalline  rocks  and  occasionally  found  massive,  is  the 
true  crystalline  mineral  apatite,  Ca5(POj3F,  in  which 
the  flourine  atom  may  be  wholly  or  partially  replaced 
by  chlorine.  This  is  a  definite  crystalline  compound, 
the  undoubted  source  of  all  the  other  compounds  of 
phosphoric   acid,  but  being  very  hard  and  difficult  of 


IV. J  THE  PHOSPHATES  OF  CALCIUM  105 

solution  in  acids  it  is  little  used  in  manure-making. 
The  typical  phosphate  of  lime,  which  is  regarded  as 
the  starting-point  for  the  manures,  is  the  tricalcium 
phosphate  CagPgOg,  which  is  supposed  to  exist  in  bone 
ash  and  in  the  natural  uncrystalline  phosphate  rock, 
such  as  is  mined  in  Algeria  or  Florida.  It  is,  however, 
doubtful  if  such  a  phosphate  really  exists  in  any  stable 
condition ;  it  has  been  shown  that  bone  ash  and  such 
phosphates,  when  treated  with  water,  continue  to  yield  a 
little  phosphoric  acid  to  solution  and  become  more  and 
more  basic ;  crystals  of  the  composition  CagPgOg  do  not 
exist,  nor  can  a  substance  corresponding  to  this  formula 
be  precipitated.  This,  however,  is  an  academic  ques- 
tion ;  in  all  dealings  with  manures  tri-calcium  phosphate 
is  supposed  to  exist,  and  whatever  the  actual  compound 
in  the  manure  may  be,  the  quantity  of  phosphoric  acid 
is  always  expressed  as  if  it  were  combined  as  tri-calcium 
phosphate.  Thus  310  parts  of  calcium  phosphate  are 
equivalent  to  142  parts  of  phosphoric  acid,  hence  what- 
ever the  percentage  of  phosphoric  acid  found  by  analysis 

it    is   multiplied    by   2- 18    {=' — )    and   expressed   as 

percentage  of  tri-calcium  phosphate.  This  puts  all 
phosphatic  manures  on  an  equal  basis  and  enables  a 
comparison  to  be  made  of  one  against  the  other,  just  as 
would  the  percentages  of  phosphoric  acid  which  are  really 
obtained  by  analysis,  but  which  are  not  in  favour  with 
manufacturers  because,  being  so  much  smaller  numbers, 
they  seem  to  give  the  manure  too  poor  a  showing. 

When  a  solution  of  phosphoric  acid,  such  as  is 
obtained  by  treating  any  of  the  natural  phosphates  with 
sulphuric  or  hydrochloric  acid,  is  precipitated  with  lime 
water,  a  salt  of  the  composition  CaHPO^,  di-calcium 
hydrogen  phosphate,  is  obtained,  and  this  is  a  perfectly 
stable  and  definite  compound.     It  sometimes  comes  on 


io6  PHOSPHATIC  MANURES  [chap. 

the  market  as  precipitated  phosphate ;  it  is  also  known 
as  retrograde  or  reverted  phosphate,  because  it  arises 
when  the  soluble  compound  next  to  be  described, 
"superphosphate,"  passes  into  the  insoluble  condition. 
When  tri-calcium  phosphate  is  treated  with  such  an 
amount  of  sulphuric  acid  as  is  required  to  combine  with 
two  out  of  the  three  lime  radicles  in  the  molecule,  a 
mixture  is  obtained  of  gypsum  and  of  soluble  mono- 
calcium  phosphate,  CaH^PgOg,  which  is  known  as 
superphosphate.  Some  uncertainty  may  still  be 
supposed  to  exist  as  to  the  exact  identity  of  this 
compound,  but  in  practice  a  readily  soluble  mixture  of 
phosphoric  acid  and  lime  in  something  like  these  pro- 
portions does  get  formed,  and  the  reactions  of  this 
solution  are  explained  accurately  enough  by  the  formula 
CaH^PgOg.  Soluble  phosphoric  acid  itself,  H3PO4,  also 
exists,  and  some  is  always  supposed  to  be  present  in  a 
free  state  in  superphosphate. 

It  has  already  been  mentioned  that  by  the  continued 
treatment  of  ordinary  insoluble  phosphates  with  water 
a  more  and  more  basic  phosphate  is  formed,  to  which 
Warington  gave  the  formula  (Cag  P208)2Ca(OH)2 ;  and  a 
definite  phosphate  of  this  type,  Ca^PgOg  or  4CaO,  PgOg, 
has  been  isolated  in  crystals  from  basic  slag  and  may  be 
supposed  to  mark  the  compound  of  lime  and  phosphoric 
acid  which  is  stable  at  high  temperatures.  It  is  this 
tetra-calcium  phosphate  which  is  supposed  to  constitute 
the  greater  part  of  the  phosphoric  acid  compounds  of 
basic  slag,  but  little  is  really  known  of  its  existence. 

Of  the  phosphatic  manures,  the  earliest  and  for  a 
long  time  the  only  ones  to  be  employed  on  a  large 
scale  were  those  derived  from  bones.  It  would  be 
impossible  to  attribute  the  discovery  of  the  fertilising 
value  of  bones  to  any  individual ;  in  common  with  all 
other  waste  materials  of  animal  origin,  they  were  prob- 


IV.]  BONES  107 

ably  tried  and  appreciated  by  numbers  of  people  in 
all  ages  and  countries;  they  are  mentioned  by  Blithe 
in  1653,  Evelyn  in  1674,  and  Worlidge  in  1668,  and  by 
the  close  of  the  eighteenth  century  their  use  was 
becoming  common  in  the  neighbourhood  of  all  the 
great  towns.  Arthur  Young  mentions  the  use  of  the 
waste  from  the  making  of  knife-handles  near  Sheffield, 
and  again  enumerates  bones  as  one  of  the  substances 
the  Hertfordshire  farmers  were  in  the  habit  of  bringing 
back  from  London  when  their  carts  had  been  delivering 
hay  or  grain,  A  Mr  St  Leger  writes  to  Dr  Hunter 
of  York  (edition  of  Evelyn's  Terra  published  in  1778): 
"  I  also  dressed  an  acre  of  grass  ground  with  bones  in 
October  1774,  and  rolled  them  in.  The  succeeding 
crop  of  hay  was  an  exceeding  good  one.  However,  I 
have  found  from  repeated  experience  that  upon  grass 
ground  this  kind  of  manure  exerts  itself  more  power- 
fully the  second  year  than  the  first.  It  must  be  obvious 
to  every  person,  that  the  bones  should  be  well  broken 
before  they  can  be  equally  spread  upon  the  land.  No 
pieces  should  exceed  the  size  of  marbles  ...  At 
Sheffield  it  has  now  become  a  trade  to  grind  bones  for 
the  use  of  the  farmer." 

It  was  in  the  early  years  of  the  nineteenth  century, 
however,  that  the  demand  began  to  grow ;  and  it  received 
a  considerable  impetus  from  the  introduction,  probably 
first  of  all  in  Yorkshire,  of  machines  for  reducing  the 
bone  into  half-  or  quarter-inch  fragments,  or  even  into 
powder.  By  181 5  the  home  supply  was  proving  insuffi- 
cient, and  bones  began  to  be  imported  from  the  Continent 
in  rapidly  increasing  quantities  until  nearly  30,000  tons 
per  annum  were  brought  in,  chiefly  from  Europe — a 
demand  which  is  said  to  have  resulted  in  the  ransacking 
of  many  of  the  battlefields.  In  this  connection  a 
characteristic     outburst    of    Liebig's    has    often    been 


io8  PHOSPHATIC  MANURES  [chap. 

quoted :  "  England  is  robbing  all  other  countries  of 
their  fertility.  Already  in  her  eagerness  for  bones, 
she  has  turned  up  the  battlefields  of  Leipsic,  and 
Waterloo,  and  of  the  Crimea :  already  from  the  cata- 
combs of  Sicily  she  has  carried  away  the  skeletons  of 
many  successive  generations.  Annually  she  removes 
from  the  shores  of  other  countries  to  her  own  the 
manurial  equivalent  of  three  million  and  a  half  of  men, 
whom  she  takes  from  us  the  means  of  supporting,  and 
squanders  down  her  sewers  to  the  sea.  Like  a  vampire 
she  hangs  upon  the  neck  of  Europe,  nay,  of  the  whole 
world,  and  sucks  the  heart  blood  from  nations  without 
a  thought  of  justice  towards  them,  without  a  shadow  of 
lasting  advantage  to  herself ! " 

For  a  time  the  importations  fell  off,  but  with  the 
growth  of  the  artificial  manure  trade  and  the  opening  up 
of  India  and  South  America  as  sources,  the  amounts 
introduced  increased  enormously,  though  since  the 
discovery  of  basic  slag  and  the  cheapening  of  mineral 
phosphates,  they  have  been  falling  greatly  again  for 
the  last  fifteen  or  twenty  years.  In  1906  the  imports 
amounted  to  42,600  tons,  the  home  production  being 
estimated  at  about  60,000  tons,  so  that  they  still  form 
a  very  important  part  of  the  fertiliser  trade,  even  if  they 
no  longer  retain  their  old  pre-eminence. 

Bones  are  but  rarely  used  for  manure  in  their  raw 
condition  as  they  are  received  from  the  collectors ;  in 
nearly  all  cases  they  are  put  through  one  or  more 
steaming  processes.  The  raw  bone  consists  of  a 
mineral  framework,  amounting  to  70  per  cent,  or 
so  of  the  dry  bone  and  consisting  in  the  main  of 
phosphate  of  lime,  which,  together  with  a  little  carbonate 
of  lime,  is  left  behind  when  the  bone  is  burnt,  as  in  bone 
ash.  The  whole  of  the  mineral  framework  is  permeated 
by   cartilage   consisting   of    nitrogenous   compounds — 


IV  ]  BONE  MANURES  lOQ 

collagen,  chondro-mucoid,  etc. — which  are  insoluble  in 
acids  and  are  left  behind  in  a  soft  tough  condition  if  the 
bone  be  put  to  soak  for  some  time  in  weak  acid.  Mixed 
with  the  cartilage  is  a  certain  amount  of  fat,  and  the 
first  treatment  the  bones  receive  is  to  steam  them 
under  a  pressure  of  15  to  20  lb.  in  order  to  melt  and 
remove  the  fat,  which  is  sold  as  tallow  or  used  for  soap- 
making  forthwith.  In  some  cases  the  fat  is  extracted 
even  more  thoroughly  by  the  action  of  benzene.  The 
boiled  or  steamed  bones  thus  obtained  contain  4  to  5 
per  cent,  of  nitrogen  and  43  to  50  per  cent,  of  calcium 
phosphate,  and  are  ready  for  conversion  into  manure. 
They  are  sometimes  merely  crushed  into  ^-inch  or  ^-inch 
bones,  though  there  is  no  longer  much  demand  for 
material  so  coarse ;  more  generally  they  are  ground 
down  into  "bone  meal."  A  really  fine  powder  is, 
however,  rarely  obtained,  because  the  cartilage  inter- 
feres materially  with  the  disintegration  unless  special 
methods  are  employed.  It  is  this  crushed  material 
which  is  also  treated  with  sulphuric  acid  for  the 
manufacture  of  "dissolved"  or  " vitriolised "  bones. 
In  factories  making  glue  the  cleaner  bones  are  picked 
out,  and,  after  the  fat  extraction,  they  are  broken  up 
and  steamed  afresh  at  a  much  higher  pressure  and 
temperature,  50  to  60  lb.  to  the  square  inch,  by  which 
process  the  collagen  takes  up  water  and  becomes  con- 
verted into  gelatine,  which  dissolves.  The  solution 
is  concentrated  and  allowed  to  set,  when  it  becomes 
glue :  the  bone  residue,  which  now  contains  only  i 
to  1-5  per  cent,  of  nitrogen  but  55  to  60  per  cent,  of 
calcium  phosphate,  is  ground  and  sold  as  "  steamed 
bone  flour."  Owing  to  the  removal  of  the  cartilage, 
this  material  can  be  ground  finely,  and  forms  a  dry 
friable  powder  very  convenient  for  use  as  a  manure. 
The  coarser  kinds  of  bone  meal  are  converted  into 


no  PHOSPHATIC  MANURES  [chap. 

dissolved  bones  by  being  mixed  with  enough  sulphuric 
acid  (see  p.  124)  to  convert  about  half  the  phosphates  into 
a  soluble  condition ;  steamed  bone  meal  is  also  often 
treated  with  acid,  but  the  product  is  not  regarded  by  the 
trade  as  dissolved  bones,  but  should  be  called  soluble 
bone  compound  or  some  other  name  not  implying  that 
it  has  been  made  from  unchanged  bones  and  acid  only. 

There  are  thus  four  classes  of  bone  fertilisers — (i) 
the  bone  itself  deprived  of  fat  and  crushed  into  the 
state  of  -l-inch  or  ^-inch  bones  or  bone  meal ;  (2) 
steamed  bone  flour,  from  which  most  of  the  nitrogenous 
material  has  been  removed ;  (3)  dissolved  bone  con- 
sisting of  No.  I  treated  with  acid  ;  (4)  bone  compound, 
generally  consisting  of  No.  2  treated  with  acid  and 
perhaps  fortified  with  nitrogen  from  some  extraneous 
source.  Table  XXXII.  shows  a  number  of  typical 
analyses  of  these  substances. 

Bone  meal,  by  far  the  most  abundant  of  these 
products,  is  a  somewhat  gritty  powder  with  a  strong 
and  distinctive  smell,  which  should  not  contain  less 
than  45  per  cent  of  calcium  phosphate.  The  per- 
centage of  nitrogen  is  more  variable :  good  fresh 
English  samples  sometimes  show  5,  but  4  per  cent, 
is  good,  and  Indian  samples  which  have  been  much 
weathered  and  are  a  little  decayed  fall  to  3  or  even 
lower;  this  nitrogen  is  not  present  in  a  very  active 
form,  the  cartilage  being  slow  to  decompose  in  the 
soil.  Of  the  phosphates  in  bones  about  one-half  can 
be  dissolved  on  shaking  up  i  gramme  of  the  bone  meal 
with  I  litre  of  i  per  cent,  citric  acid  solution,  which 
would  show  that  the  phosphoric  acid  is  easily  available. 
However,  there  is  plenty  of  experimental  evidence  that 
bone  meal  is  rather  slow  acting  as  a  source  of  phosphoric 
acid,  probably  because  of  its  comparative  coarseness 
and    the    consequent    small    surface    of    the    manure 


IV.] 


nONE  MANURES 


ttt 


particles  offered  to  the  solvent  action  of  the  soil  water ; 
and  it  is  the  appreciation  of  this  fact,  and  the  rise  of 
other  phosphatic  manures  like  basic  slag,  which  have 
caused  the  decline  in  recent  years  of  the  popularity  of 


Table  XXXII.— Composition 

OF  Bones  and  Bone  Manures. 

a 

1 

0  . 

0.-3 

0 

phoric 
cid. 

■alent  to 

alcium 

ipliate. 

g 

§0 

3-r  — 

§<1 

—  V  0 

Oh 

H^^ 

P^ 

|g£ 

Raw  Bones  : — 

Not  degreased     . 

4-45 

20'14 

43-98 

... 

... 

11                *        • 

5<3I 

22-00 

48-03 

... 

,,                 ,         , 

4-o6 

23-36 

51-01 

... 

Bone  Meal:— 

Fat  extracted 

4-94 

22-81 

49-80 

... 

... 

11                 •        • 

5-17 

22-46 

49-03 

... 

Steamed      .         . 

4-59 

22-09 

48-23 

11            •         ,        . 

4-5° 

21-48 

46-92 

Indian 

3-35 

23-19 

50-62 

11               ... 

3-6 

22-6 

49-35 

Steamed  Bone  :— 

Meal  .... 

0-93 

29-02 

63-36 

..-• 

Flour. 

1-34 

28-27 

61-72 

... 

... 

„     .         .         .         . 

104 

31-5 

68-76 

... 

Solu 

ble. 

Insol 

uble. 

Dissolved  Bones  :— 
From  raw  bone   . 

2-92 

5-59 

12-2 

11-57 

25-25  1 

i»             11         •         • 

3-21 

5-10 

11-64 

12-23 

26-69  j 

i»            )»         •         • 

3-44 

4-84 

10-54 

II -06 

24-12     i 

>»            II         •         • 

2-96 

6-91 

15-0S 

10-40 

21-93    1 

«»            11         •         • 

3-47 

7-84 

17-13 

9-44 

20-62    i 

„     boiled  bone 

1-33 

4-58 

9-99 

8.28 

17-90 

II              11               • 

1.42 

8.96 

19-55 

3-83 

8-38  j 

Bone  Compound  . 

0-82 

8-5 

18-55 

5.. 

11-35 

bone  meal.  It  was,  however,  bones  in  their  even  coarser 
form — merely  roughly  broken,  sometimes  by  hand  on 
the  farm — which  built  up  the  fertility  of  much  English 
land,  as,  for  instance,  the  famous  dairy  pastures  of 
Cheshire,   which   were   made   during   the    early  years 


112  PHOSPHATIC  MANURES  [chap. 

of  the  nineteenth  century.  Large  dressings  of  bones 
were  employed — a  ton  or  more  per  acre — and  the 
application  was  expected  to  last  for  twenty  years, 
little  return  being  obtained  during  the  first  year  or 
two ;  for  this  reason  the  landlord  contributed  freely 
to  the  cost  of  boning,  even  if  he  did  not  pay  for  it 
entirely.  The  pastures  improved  steadily  after  the 
dressing  of  bones ;  in  particular,  such  a  growth  of 
white  clover  was  encouraged  that  farmers  began  to 
suspect  the  manure  contained  clover  seed,  a  supposition 
which  was  repeated  fifty  years  or  more  later  when  basic 
slag  first  began  to  be  used  on  clay  pastures.  At  one 
time  bones  and  bone  meal  were  subject  to  a  good  deal 
of  adulteration,  often  of  the  most  flagrant  description ; 
nowadays,  however,  there  is  very  little  admixture  of 
foreign  substances  with  bone  meal.  Occasionally  mineral 
phosphates  may  be  used  to  raise  the  percentage  of  phos- 
phoric acid,  or  the  bone  meal  may  be  represented  as 
richer  than  it  is,  but  these  frauds  are  at  once  detected 
on  analysis,  which  indeed  should  never  be  omitted 
because  of  the  natural  variations  in  the  material. 

If  bone  meal  is  still  somewhat  overvalued  on  account 
of  the  long  experience  farmers  have  had  of  its  value, 
on  the  other  hand,  steamed  bone  flour  hardly  gets 
justice  done  to  it.  Its  deficiency  in  nitrogen  is  regarded 
as  a  defect,  but  when  steamed  bone  flour  is  considered 
merely  as  a  phosphatic  manure,  its  finer  grinding  and 
freedom  from  cartilage  render  it  more  available  than 
bone  meal  ever  can  be.  The  experiments  of  the  High- 
land and  Agricultural  Society  during  1 890-1  have  shown 
it  to  be  about  the  most  suitable  of  all  the  phosphatic 
manures  for  the  turnip  crop  on  light  soils  which  are  too 
poor  in  lime  for  superphosphate  and  too  short  of  water 
for  basic  slag.  For  the  sands  and  gravels,  a  neutral 
easily  soluble  manure  like  steamed  bone  flour  is  the  best 


IV.]  DISSOLVED  BONES  113 

form  of  applying  phosphates;  a  mixture  of  steamed 
bone  flour  and  superphosphate  left  for  a  few  days 
in  the  mixing  shed  and  then  broken  down  again 
is  also  very  useful  on  such  land. 

Dissolved  bones  also  represents  a  manure  which  at 
one  time  had  a  much  greater  vogue  than  it  possesses 
at  the  present  day,  when  it  is  no  longer  admitted 
that  superphosphate  made  from  bone  possesses  any 
superiority  over  the  same  compound  made  from 
mineral  phosphates,  except  in  so  far  as  the  bone 
manure  also  contains  nitrogen.  Dissolved  bones  or 
bone  superphosphate  generally  contains  from  35  to  40 
per  cent,  of  phosphate,  of  which  from  12  to  18  will 
usually  be  in  a  soluble  condition ;  while  the  nitrogen 
amounts  to  about  3  per  cent. 

Dissolved  bones  forms  a  brown  mass  generally 
somewhat  damp  and  sticky,  and  not  rubbing  down 
into  a  convenient  powder  for  sowing;  it  is,  in  fact, 
impossible  to  get  it  into  a  dry  friable  condition 
without  some  admixture  of  "  dryers "  like  gypsum, 
which  are  not  considered  as  admissible.  The  trade 
in  dissolved  bones  usually  proceeds  on  a  guarantee 
that  it  contains  pure  bones  and  sulphuric  acid  only, 
though  it  is  difficult  to  demonstrate  that  such  a 
product  possesses  any  intrinsic  superiority  over  any 
other  manure  mixture  compounded  so  as  to  show 
the  same  composition.  Such  mixtures  are  furnished 
by  the  bone  compounds  and  bone  manures,  which 
are  often  mineral  superphosphates  mixed  with  more 
or  less  superphosphate  made  from  steamed  bone 
flour,  with  a  little  extra  nitrogen  derived  from  dried 
blood,  fine  shoddy,  or  even  sulphate  of  ammonia. 
Such  compounds  are  useful  enough  if  they  are  cheap ; 
before  purchase  they  should  be  valued  on  the  basis  of 
their  analysis  and  judged  accordingly^ 

H 


114  PHOSPHATIC  MANURES  [chap. 

Mineral  Phosphates. 

With  the  recognition  that  the  fertiHsing  value  of 
bones  lay  in  the  phosphate  of  lime  they  contained, 
which  we  may  conclude  had  become  the  accepted 
opinion  about  1840,  attention  began  to  be  directed  to 
mineral  sources  of  phosphate  of  lime, — apatite  and 
phosphorite,  the  existence  of  which  had  long  been 
known  to  mineralogists.  Acting  on  an  analysis  of 
Proust's,  Professor  Daubeny  and  Captain  Widdrington 
made  an  expedition  in  1843  to  Estremadura  to  find  a 
bed  of  phosphatic  rock  there  reported.  They  dis- 
covered the  deposit  and  secured  enough  of  it  for  a  few 
field  experiments  in  England  in  the  following  year, 
but  difficulties  of  transport  prevented  anything  more 
than  small  quantities  being  exported  until  a  much  later 
period.  The  immediate  demand  for  such  material  was 
satisfied  by  the  discovery  in  1845  by  Professor  Henslow 
of  the  bed  of  coprolites  lying  at  the  base  of  the  Green- 
sand  near  Cambridge. 

These  coprolites — small  rounded  nodules  of  impure 
phosphate  of  lime,  mixed  with  fragments  of  bone  and 
shell,  shark's  teeth,  etc. — were  at  one  time  regarded  as 
fossilised  dung,  but  are  now  considered  to  be  pebbles  of 
carbonate  of  lime  in  which  the  carbonic  acid  has  been 
replaced  by  phosphoric  acid  by  long  contact  with 
material  containing  organic  matter.  They  occur  at 
various  horizons  in  the  newer  secondary  and  tertiary 
rocks,  e.g.,  at  the  base  of  the  Upper  Greensand  and  at  the 
base  of  the  Gault,  and  in  the  Crag,  where  it  rests  upon 
the  London  Clay.  Shortly  after  their  discovery  these 
deposits  began  to  be  worked  for  coprolites  at  various 
places  in  Suffolk,  near  Cambridge,  and  at  Potton  in 
Bedfordshire.  The  output  reached  50,000  tons  or  so 
in  the  early  eighties  of  the  last  century,  but  then  rapidly 


IV.]         cor  ROUTES  AND  ROCK  PHOSPHA  TE  115 

declined  owing  to  the  opening  up  of  so  many  cheaper 
foreign  deposits,  and  has  of  late  }'ears  entirely  ceased. 
The  coprolites  formed  hard  dark-coloured  nodules,  which 
were  ground  down  to  a  grey  powder  containing  from  50 
to  60  per  cent,  of  calcium  phosphate,  about  10  per  cent, 
of  calcium  carbonate,  and  3  per  cent,  of  calcium  fluoride. 
Though  occasionally  applied  directly  to  the  land  in  a 
ground  form,  they  were  almost  wholly  used  in  the 
manufacture  of  superphosphate. 

Another  phosphatic  material  which  is  practically 
mineral  and  at  one  time  entered  into  competition 
with  coprolites  and  bone  phosphates  as  material  for  the 
manufacture  of  superphosphate,  consists  of  these  guano 
deposits  in  which  the  nitrogen  has  been  wholly  removed 
or  nearly  so  by  the  action  of  rain.  Such  deposits  are 
found  in  the  West  Indies  (Aruba,  Navassa,  Sombrero, 
Curacao),  the  Pacific  (Baker,  Abrolhos,  Christmas,  and 
Ocean  Islands),  Bolivia  (Mejillones),  and  one  or  two 
other  places  'of  less  importance.  The  action  of  the 
weather,  particularly  where  the  climate  is  not  absol- 
utely rainless,  is  always  removing  the  nitrogenous 
compounds  from  guano,  so  that  the  proportion  of 
phosphoric  acid  tends  to  increase,  until  even  among 
the  Peruvian  deposits  a  guano  is  found  on  Lobos 
Island  containing  little  more  than  2  per  cent,  of 
nitrogen  and  60  per  cent,  of  phosjDhate  of  lime.  In 
some  of  the  other  deposits  that  have  been  enumerated, 
Christmas  Island  for  example,  the  nitrogen  has  entirely 
disappeared  and  a  phosphate  rock  is  left  behind  which 
can  only  be  termed  a  guano  in  virtue  of  its  origin. 
These  purely  phosphatic  deposits,  many  of  which  are 
now  exhausted  or  no  longer  pay  to  work,  have  been  so 
much  mineralised  that  they  are  not  sold  as  guanos  but 
are  employed  for  the  manufacture  of  superphosphate. 
However,  the  Lobos  phosphatic  guano  is  still   exten- 


ri6  PHOSPHATIC  MANURES  [chap. 

sively  imported,  and  being  naturally  soft  and  in  a  fine 
state  of  division,  it  can  be  applied  without  treatment  to 
the  land,  and  forms  one  of  the  most  valuable  of  the 
neutral  phosphates  that  are  so  well  adapted  to  light 
soils.  With  the  exception  of  the  Peruvian  deposits  and 
those  from  the  Pacific — Christmas  and  Ocean  Islands, 
practically  none  of  the  other  deposits  are  now  worked. 

While  some  of  these  "crust  guanos,"  as  they  were 
termed,  contained  high  percentages  of  phosphoric  acid, 
the  presence  of  oxides  of  iron  and  aluminium  in 
quantity  seriously  interfered  with  the  use  of  the  Aruba 
and  Navassa  rock  as  material  for  superphosphate  making. 

More  akin  to  the  English  coprolites  were  the  phos- 
phates obtained  from  France,  Germany,  and  Belgium, 
where  they  occur  in  the  secondary  and  tertiary  forma- 
tions on  a  more  important  scale  than  do  the  similar 
deposits  in  England.  Of  these  materials  the  most 
important  were  the  Lahn  phosphates,  extensively 
worked  for  some  time  after  their  discovery  in  1864,  the 
Belgian  phosphates  worked  near  Mons,  with  45  to  60 
per  cent,  of  phosphate  of  lime,  and  the  Somme  phos- 
phates, of  which  extensive  deposits  were  found  in  the 
north  of  France,  and  formed  an  important  source  of 
supply  to  the  manure  market  about  1890. 

The  Lahn  phosphates  fell  out  of  favour  because  of 
the  large  amount  of  iron  and  alumina  they  contained, 
the  Belgian  phosphates  became  of  too  low  grade,  but 
the  Somme  phosphates  remained  valuable  because  they 
contained  in  the  better  grades  70  per  cent,  or  so  of 
phosphate  of  lime,  and  only  i  to  2  per  cent,  of  oxides 
of  iron  and  alumina.  They  also  yielded  a  very  dry  and 
friable  superphosphate,  and  were  useful  for  mixing 
with  the  Florida  phosphates  before  treatment  with  acid. 
These  coprolitic  phosphates,  however,  attain  their 
greatest  development  in  Florida,  Tennessee,  and  South 


IV.]  ROCK  PHOSPHATES  117 

Carolina.  There  in  many  places  the  subsoil  is  a  sandy- 
deposit  full  of  coprolitic  pebbles,  which  can  readily  be 
separated  by  screens  or  washing  ;  the  beds  of  the  rivers 
and  creeks,  again,  are  wholly  composed  of  the  same 
pebbles,  which  are  recovered  by  dredging.  The  land 
phosphate  contains  some  oxide  of  iron  and  alumina,  and 
is  chiefly  sold  in  the  United  States,  but  the  river 
deposits  have  been  particularly  valued  in  Great  Britain 
for  superphosphate  making,  because  though  they  only 
contained  about  60  per  cent,  of  phosphate  of  lime  they 
were  specially  free  from  iron  and  alumina.  About 
1 50,000  tons  per  annum  used  to  be  imported,  but  of  late 
years  the  supply  has  been  falling  off.  The  various 
phosphate  deposits  in  North  America  yielded  in  1901 
nearly  1,600,000  tons,  of  which  more  than  half  was 
exported  to  Europe. 

Just  as  it  is  impossible  to  draw  a  line  between  the 
recently  formed  true  guanos  and  the  weathered  deposits 
which  have  practically  become  phosphate  rock,  so  again 
no  real  distinction  can  be  made  between  the  guanos  and 
coprolites  of  known  origin  and  the  phosphate-bearing 
strata  which  are  to  be  found  in  many  countries  and  at 
all  geological  horizons.  Many  of  these  may  have 
originated  in  guano  beds,  others  are  coprolitic,  others 
again  are  due  to  solution  of  phosphate  of  lime,  originally 
diffused  through  a  great  mass  of  rock,  and  its  concentra- 
tion in  a  single  layer.  In  all  cases,  however,  the  material 
has  been  of  animal  origin,  whatever  processes  of  solution 
and  redeposition  it  may  have  suffered  since.  In  the  older 
rocks  the  phosphate  has  often  become  crystalline,  forming 
the  hard  mineral  known  as  apatite,  which  is  mined  on  a 
small  scale  in  Canada  and  Norway.  The  Estremadura 
deposits  were  perhaps  the  first  of  the  rock  phosphates 
to  be  described,  though  they  were  not  much  worked 
until  the  seventies  of  the  last  century. 


ii8  PnOSPHATIC  MANURES  [chap. 

All  these  phosphate  deposits  are  now  yielding  to 
the  competition  of  the  great  deposits  of  phosphate 
rock  which  have  been  discovered  in  Northern  Africa 
and  are  now  being  exported  in  immense  quantities 
from  Algeria  and  Tunis.  The  phosphate  bed  appears 
to  stretch  right  across  the  continent,  but  Morocco  has, 
naturally,  not  been  explored,  while  the  Egyptian  rocks 
as  yet  examined  are  hardly  rich  enough  in  phosphoric 
acid  for  export,  though  immense  beds  exist  containing 
40  to  50  per  cent,  of  tricalcium  phosphate.  The  most 
important  of  the  phosphate  mines  in  North  Africa  occur 
in  the  province  of  Constantino  in  the  district  of  Tebessa, 
from  whence  they  extend  into  Tunis,  near  Gafsa.  The 
rock  is  generally  at  the  base  of  the  Eocene  system,  and 
occurs  in  strata  that  may  be  2J  or  3  metres  thick  and 
contain  as  much  as  60  per  cent,  of  calcium  phosphate, 
which  may  be  raised  to  70  per  cent,  by  picking 
over.  These  African  phosphates  contain  but  little  iron 
and  alumina,  and  are  rapidly  becoming  the  chief 
material  for  the  manufacture  of  superphosphate  in  this 
country. 

The  mineral  phosphates  have  been  but  little 
employed  directly  as  manures,  though  there  is  plenty 
of  evidence  that  when  they  are  really  finely  ground 
they  are  effective  enough  on  soils  retaining  plenty  of 
water,  and  particularly  on  those  of  a  peaty  nature. 
Recent  experiments  also  indicate  that  such  ground 
mineral  phosphates  are  most  available  when  used 
with  ammonium  sulphate,  which,  as  already  explained, 
acts  as  a  physiologically  acid  manure  and  helps  to 
bring  the  phosphoric  acid  into  solution.  In  the  main, 
however,  the  mineral  phosphates  are  used  for  the 
manufacture  of  superphosphate,  practically  the  only 
manure  which  contains  phosphoric  acid  at  all  readily 
soluble  in  water. 


IV.]  SUPERPHOSPHATE  119 

Superphosphate. 

In  the  early  years  of  the  nineteenth  century,  long 
prior  to  the  introduction  of  superphosphate  as  a 
manure,  the  existence  of  a  soluble  phosphate  of  lime 
produced  by  the  action  of  sulphuric  acid  upon  bone  ash 
was  a  matter  of  common  chemical  knowledge,  and  the 
composition  of  this  and  the  other  phosphates  had  been 
studied  accurately  by  Berzelius.  The  application  of 
this  knowledge  to  agriculture  and  the  introduction  of 
superphosphate  as  an  artificial  manure  began  about 
1840.  The  first  published  suggestion  of  the  kind  is 
due  to  Liebig,  in  1840,  in  his  Report  to  the  British 
Association,  which  was  published  in  the  September 
of  that  year  as  TJie  Chemistry  of  Agriculture  and 
Physiology.  Writing  of  bones  as  a  manure  and  the 
necessity  of  their  being  finely  divided,  he  goes  on : — 
"  The  most  easy  and  practical  mode  of  effecting  their 
division  is  to  pour  over  the  bones,  in  a  state  of  fine 
powder,  half  of  their  weight  of  sulphuric  acid,  diluted 
with  three  or  four  parts  of  water ;  and  after  they  have 
been  digested  for  some  time  to  add  100  parts  of  water, 
and  sprinkle  this  mixture  over  the  field  before  the 
plough.  In  a  few  seconds  the  free  acids  unite  with  the 
bases  contained  in  the  earth,  and  a  neutral  salt  is 
formed  in  a  very  fine  state  of  division.  Experiments 
instituted  on  a  soil  formed  from  a  Grauwacke,  for  the 
purpose  of  ascertaining  the  action  of  manures  thus 
prepared,  have  distinctly  shown  that  neither  corn  nor 
kitchen  garden  plants  suffer  injurious  effects  in  conse- 
quence, but  that,  on  the  contrary,  they  thrive  with  much 
more  vigour."  Liebig  then  adds : — "  In  the  manu- 
factories of  glue,  many  hundred  tons  of  a  solution  of 
phosphates  in  muriatic  acid  are  yearly  thrown  away  as 
being  useless.  ...  It  would  be  important  to  examine 


I20  PHOSPHATIC  MANURES  [chap. 

whether  this  solution  might  not  be  substituted  for  the 
bones." 

In  1 841,  a  Mr  Fleming  of  Barrochan  had  made  an 
experiment  with  about  three-quarters  of  a  pound  of 
dissolved  bones,  and  in  1842  the  Highland  and  Agri- 
cultural Society  offered  a  prize  for  an  experiment  with 
bones  dissolved  in  sulphuric  acid.  In  January  1842, 
Professor  Johnston,  in  his  published  lectures,  suggested 
the  use  for  purposes  of  manure  of  acid  or  soluble 
phosphate  of  lime,  made  by  adding  sulphuric  acid  to 
burnt  bones  or  bone  ash: — '^ Acid  or  biphosphate  of 
lime. — When  burned  bones  are  reduced  to  powder,  and 
digested  in  sulphuric  acid  (oil  of  vitriol)  diluted  with 
once  or  twice  its  weight  of  water,  the  acid  combines 
with  a  portion  of  the  lime,  and  forms  sulphate  of  lime 
(gypsum),  while  the  remainder  of  the  lime  and  the 
whole  of  the  phosphoric  acid  are  dissolved.  The 
solution,  therefore,  contains  an  acid  phosphate  of  lime, 
or  one  in  which  the  phosphoric  acid  exists  in  much 
larger  quantity  than  in  the  earth  of  bones.  "If  the 
mixture  of  gypsum  and  acid  phosphate  above  described 
be  largely  diluted  with  water,  it  will  form  a  most 
valuable  liquid  manure,  especially  for  grass  land  and  for 
crops  of  rising  corn.  In  this  liquid  state,  the  phosphoric 
acid  will  diffuse  itself  easily  and  perfectly  throughout 
the  soil,  and  there  will  speedily  lose  its  acid  character 
by  combining  with  one  or  other  of  the  basic  substances, 
almost  always  present  in  every  variety  of  land."  Mr 
Hannam  in  Yorkshire,  in  1843,  claimed  to  have  been 
the  first  to  carry  out  this  experiment  with  burnt  bones 
and  acid. 

All  these  experiments,  however,  had  in  reality  been 
anticipated  by  Mr  J.  B.  Lawes,  to  whom,  in  May  1842, 
was  granted  a  patent  for  making  superphosphate,  from 
the   specification   of  which   the   following   extract  has 


IV.]      EARL  Y  HISTOR  Y  OF  SUPERPHOSPHA TE      121 

been  made ; — "  Whereas  bones,  bone  ash,  and  bone 
dust  and  other  phosphoritic  substances  have  been 
heretofore  employed  as  manures,  but  ahvays,  to  the  best 
of  my  knowledge,  in  a  chemically  undecomposed  state, 
whereby  their  action  on  the  soils  to  which  they  have 
been  applied  has  been  tardy  and  imperfect.  And 
whereas  it  is  in  particular  well  known  that  in  the  case 
of  a  large  proportion  of  the  soils  of  this  country,  the 
application  of  bone  dust  is  of  no  utility  in  producing 
crops  of  turnips  on  account  of  the  slow  decomposition  of 
the  bone  dust  in  the  soil,  and  the  consequent  exposure 
of  the  young  plant  for  a  long  period  to  the  ravages  of 
the  turnip  fly.  Now,  the  first  of  my  said  improvements 
consists  in  decomposing,  in  manner  following,  the  said 
bones,  bone  ash,  bone  dust,  and  other  phosphoritic 
substances.  Previous  to  using  them  for  the  purposes 
of  manure,  I  mix  with  the  bones,  bone  ash,  or  bone 
dust,  or  with  apatite  or  phosphorite,  or  any  other 
substance  containing  phosphoric  acid,  a  quantity  of 
sulphuric  acid  just  sufficient  to;  set  free  as  much 
phosphoric  acid  as  will  hold  in  solution  the  unde- 
composed phosphate  of  lime." 

Subsequently,  on  becoming  acquainted  with  Liebig's 
published  suggestion,  Lawes  amended  his  patent  by 
disclaiming  all  references  to  bone  and  bone  products, 
and  confining  it  to  "apatite  and  phosphorite,  and 
other  substances  containing  phosphoric  acid."  Follow- 
ing on  his  patent,  Lawes  began  the  manufacture  of 
superphosphate  on  a  commercial  scale,  establishing  a 
factory  at  Deptford  and  using  for  the  purpose  at  first 
bone  ash  and  later  the  crag  coprolites  from  Suffolk,  to 
which  Henslow's  paper  in  1845  had  attracted  attention. 
The  first  advertisement  appears  in  the  Gardetier's 
Chronicle  and  Agricultural  Gazette  in  1843,  the  price 
being  4s.  6d.  per  bushel.     From  the  dates  of  Liebig's 


122  PHOSPHATIC  MANURES  [chap. 

book  and  Lawes'  patent,  Liebig  has  generally  been 
regarded  as  the  inventor  of  superphosphate,  and  even 
though  Lawes  was  able  to  take  out  a  patent  for  making 
it  from  mineral  phosphates  instead  of  from  bones,  the 
idea  is  generally  set  down  to  Liebig.  Owing,  however, 
to  actions  for  infringement  of  his  patent  brought  by 
Lawes  in  1853,  the  steps  leading  up  to  Lawes'  patent 
are  on  record,  and  it  is  seen  that  he  arrived  at  the  idea 
of  making  superphosphate  and  had  tried  it  experi- 
mentally on  a  considerable  scale,  prior  to  Liebig's 
publication. 

In  his  proof  of  evidence,  Lawes,  after  describing  his 
fitting  up  of  a  laboratory  and  taking  over  the  Rothamsted 
estate  in  1834,  stated  that  during  1836,  1837,  and  1838, 
he  used  considerable  quantities  of  bone  dust  on  his 
farm  for  the  purpose  of  manuring  his  turnip  crops,  and 
finding  that  it  produced  no  good  effects,  and  knowing 
that  upon  other  soils  its  properties  as  a  manure  were 
very  great,  he  commenced  a  series  of  experiments 
with  bones  and  mineral  phosphate  of  lime  decomposed 
by  sulphuric  and  other  acids,  applied  to  the  most 
important  agricultural  plants  of  the  farm.  These 
experiments  were  in  1839  conducted  on  a  small  scale 
by  plants  in  pots  and  by  manuring  a  certain  number 
of  plants  in  a  field.  The  result  of  these  small  experi- 
ments was  most  remarkable  with  turnips,  and  he 
in  1840  used  the  superphosphate  on  half  an  acre  or 
more  of  that  crop.  In  1841  the  results  were  so  far 
advanced  that  he  used  about  20  tons  of  superphosphate. 
He  was  prepared  to  have  taken  out  a  patent  in  1841, 
but  was  persuaded  by  his  friends  not  to  do  so,  as  they 
objected  to  his  embarking  in  any  mercantile  or  business 
occupation  (Lawes  was  then  only  twenty-six  years  of 
age).  Lawes  further  stated  that  he  had  not  noticed 
Liebig's  recommendation    until  after  the   date  of  his 


IV.]      EARLY  HISTORY  OF  SUPERPHOSPHATE      123 

patent,  whereupon  he  disclaimed  the  use  of  bone 
substances  included  therein.  He  also  declared  that  he 
began  his  manufacture  with  bone  ash,  apatite  and 
phosphorite  being  unobtainable  commercially,  though 
in  1843  he  imported  several  tons  of  the  Spanish 
phosphorite  from  Estremadura,  and  early  in  1845  began 
his  enquiries  if  coprolites  could  be  obtained  cheaply 
from  the  Eastern  counties.  Gilbert  also  gave  evidence 
that  the  manufacture  and  use  of  superphosphate  on 
a  large  scale  prior  to  the  date  of  the  patent  were 
matters  of  common  knowledge  at  Rothamsted  when 
he  came  there  in  1843.  Putting  aside  the  fact  that 
Lawes  was  the  iirst  man  to  make  superphosphate  a 
practical  possibility,  there  is  thus  no  doubt  that 
he  arrived  at  the  idea  of  the  importance  of  a  soluble 
phosphatic  manure  quite  independently  of  Liebig, 
and  had  tested  the  idea  on  a  working  scale  before 
taking  out  his  patent.  The  only  other  point  of 
interest  in  this  early  history  of  superphosphates  is  that 
Sir  James  Murray  of  Dublin  took  out  a  patent  a  few 
weeks  before  Lawes,  in  which  he  suggested  as  manure 
phosphoric  acid  prepared  by  treating  phosphorite  with 
sulphuric  acid  Murray's  object,  however,  was  to 
generate  carbonic  acid  in  the  ground,  and  his  patent  is 
for  a  means  of  "  mechanically  fixing  and  solidifying 
mineral  acids " — sulphuric,  muriatic,  nitric,  and  phos- 
phoric— by  mixing  them  with  absorbent  matter  like 
bran,  sawdust,  peat,  etc.,  the  phosphoric  acid  thus 
coming  in  incidentally  only,  and  not  for  its  own 
nutritive  value  to  plants.  A  few  years  later,  to  avoid 
any  question  of  priority  that  might  arise,  Lawes 
purchased  Murray's  patent,  and  amended  it  by  dis- 
claiming everything  but  the  manufacture  of  a  manure 
by  the  treatment  of  phosphorite  with  acid. 

The   early   superphosphate   thus   manufactured    by 


124  PHOSPHATIC  MANURES  [chap. 

Lawes  and  sold  at  about  £'j  a  ton,  was  a  mixture  of 
soluble  and  insoluble  phosphate  derived  from  coprolites 
or  from  guanos,  mixed  with  animal  substances  and  am- 
moniacal  salts,  resembling,  in  fact,  dissolved  bones  and 
very  much  the  kind  of  thing  nowadays  sold  as  soluble 
bone  compound.  Way  in  1851  gives  analyses  ranging 
from  3-24  to  0-I2  per  cent,  of  nitrogen,  soluble  phosphate 
of  lime  from  18-5  down  to  i-6  per  cent.,  insoluble  from 
28-3  down  to  o-o6  per  cent.  By  1862  the  manufacture 
had  risen  to  150,000  to  200,000  tons  per  annum  ;  in  1907 
about  700,000  to  800,000  tons  were  made  in  the  United 
Kingdom,  of  which  about  120,000  tons  were  exported. 

In  the  manufacture  of  superphosphate,  the  finely- 
ground  materials,  graded  and  mixed  after  analysis  so  as 
to  produce  superphosphate  of  the  desired  quality,  are 
mixed  with  sufificient  dilute  oil  of  vitriol,  containing 
about  60  per  cent  of  pure  acid,  to  bring  about  the 
following  reaction  :-— 

Ca3P208  +  2H2S04  +  4H20  =  CaH^PgOg  +  sCaSO^,  2H2O. 

At  the  same  time,  an  excess  of  acid  must  also  be  em- 
ployed to  convert  into  sulphates  the  carbonate,  fluoride, 
and  chloride  of  calcium  present.  The  mixing  is  per- 
formed mechanically,  a  considerable  rise  of  temperature 
ensues,  and  there  is  an  evolution  of  water  vapour,  car- 
bonic, hydrochloric,  and  hydrofluoric  acids ;  the  two  latter, 
besides  causing  a  waste  of  sulphuric  acid,  are  trouble- 
some to  the  manufacturer,  because  they  must  be  con- 
densed, and  not  allowed  to  escape  into  the  atmosphere. 
After  mixing,  the  hot  damp  mass  is  dropped  into  a 
lower  chamber  where  the  reaction  completes  itself,  and 
the  whole  solidifies  as  the  gypsum  combines  with  the 
remaining  water.  The  mass  is  easily  friable,  and  is 
dug  out,  crushed,  and  put  into  store.  At  one  time 
artificial  drying  had  to  be  employed,  in  order  to  obtain 


IV.]  COMPOSITION  OF  SUPERPHOSPHATE         125 

a  really  dry  product  that  would  run  easily  through  a 
drill,  but  all  necessity  for  that  process  has  passed  away 
since  high  grade  phosphates  containing  but  little  iron 
or  alumina  have  been  available.  The  more  gypsum  the 
finished  "  super "  contains,  the  drier  and  more  friable 
the  powder,  hence  the  former  value  of  Somme  phosphate 
for  mixing  purposes,  because  its  impurity  was  almost 
wholly  calcium  carbonate.  The  objection  of  the  super- 
phosphate maker  to  oxides  of  iron  and  aluminium  in 
the  raw  material  arises  from  two  sources — the  bad 
mechanical  condition  of  the  resulting  compound  and 
its  tendency  to  revert.  In  calculating  the  amount  of 
sulphuric  acid  to  use,  a  little  calcium  phosphate  is 
always  left  undecomposed,  because  free  phosphoric 
and  sulphuric  acids  would  injure  the  mechanical  con- 
dition of  the  fertiliser.  This  phosphate  of  lime  left 
unattacked  will  always  slowly  combine  with  some  of 
the  acid  phosphate  to  form  two  molecules  of  the 
intermediate  di-calcium  phosphate,  which  is  thus  known 
as  reverted  or  retrograde  phosphate — 

CaH^PaOg  +  CagPgOg  =  2Ca2H2P208. 

Since  this  last  compound  is  insoluble  in  water,  freshly 
made  superphosphate  always  contains  a  little  more 
phosphoric  acid  soluble  in  water  than  it  does  after  it 
has  been  stored  for  some  time,  and  as  in  England  this 
fertiliser  is  valued  only  on  the  basis  of  its  water  soluble 
phosphoric  acid,  to  this  extent  it  deteriorates  on  storage. 
The  deterioration  is  more  pronounced  when  the 
raw  material  contains  oxides  of  iron  and  aluminium, 
because  both  of  these  substances  will  slowly  react  with 
acid  phosphate  to  form  insoluble  phosphates  of  iron  or 
aluminium.  Even  if  these  oxides  have  been  attacked 
by  the  sulphuric  acid  to  form  ferric  or  aluminium 
sulphates,  or  if  the  iron  and  aluminium  were  originally 


126  PHOSPHATIC  MANURES  [chaP. 

present  as  phosphates,  which  by  treatment  with  the 
acid  give  rise  to  sulphates  of  these  metals  and  free 
phosphoric  acid,  reversion  will  still  take  place  at  the 
lower  temperatures.  A  mixture  of  ferric  sulphate  and 
phosphoric  acid  is  not  stable,  but  will  always  partly  go 
back  to  ferric  phosphate  and  sulphuric  acid,  the  final 
state  of  equilibrium  which  is  attained  being  one  with  a 
large  proportion  of  insoluble  ferric  phosphate.  It  is 
for  this  reason  that  so  much  stress  is  laid  in  the  United 
Kingdom  on  raw  phosphates  being  free  from  iron  and 
aluminium  ;  on  the  Continent,  where  reverted  phosphate 
(estimated  by  solubility  in  ammonium  citrate  or  2  per 
cent,  solution  of  citric  acid)  is  ranked  as  almost  the 
equal  of  water  soluble  phosphate,  there  is  not  the  same 
objection  to  the  use  of  such  materials. 

Superphosphate  as  manufactured  nowadays  is  a  grey 
friable  powder,  which  is  made  in  various  grades  contain- 
ing 26,  30,  35  and  40  per  cent,  of  phosphate  made  soluble 
or  12,  14,  16,  and  18  respectively  of  phosphoric  acid, 
together  with  about  2  per  cent,  of  insoluble  phosphate. 
The  26  per  cent,  super  has  for  long  been  the  standard 
article  and  is  still  the  most  generally  manufactured, 
because  a  good  dry  product  can  be  made  from  the 
raw  phosphates  most  readily  available,  whereas  the 
higher  grades  require  selected  materials  if  the  result 
is  to  be  dry.  They  were,  in  fact,  chiefly  made  for 
export,  but  since  they  are  now,  owing  to  the  better 
quality  of  the  raw  phosphates  available,  just  as  cheap 
per  unit  of  phosphoric  acid  as  the  lower  grades,  there  is 
every  reason  for  saving  carriage  by  their  purchase. 

The  chief  phosphates  at  present  employed  for 
superphosphate-making  are  those  from  North  Africa 
— Tocqueville,  Gafsa,  Tebessa,  and  Algerian — Florida 
hard  rock  and  pebble,  Christmas  Island  phosphate,  and 
the  Aruba  and  Carolina  deposits.    The  material  is  ground 


IV.]  BASIC  SLAC^  127 

until  80  per  cent,  passes  through  a  sieve  with  100 
meshes  to  the  inch,  the  African  phosphates  being  much 
easier  to  grind  than  those  from  Florida,  and  then  it  is 
mixed  with  about  70  per  cent,  of  chamber  acid  of  a 
specific  gravity  1-52,  according  to  the  composition  of 
the  rock.  The  mass  takes  a  day  or  two  to  cool,  is 
disintegrated  and  thrown  into  heaps,  after  which  it 
must  be  crushed  again  before  it  is  bagged.  About 
half  a  ton  of  acid  is  used  in  making  a  ton  of  super. 

The  next  great  development  in  regard  to  phos- 
phatic  manures  came  from  a  very  unexpected  source — 
the  introduction  of  basic  slag  as  a  waste  product  in 
steel-making.  A  great  many  ores  of  iron,  notably  those 
found  in  the  Cleveland  district  of  North  Yorkshire, 
contain  considerable  quantities  of  phosphates,  and  in 
the  process  of  smelting  in  the  ordinary  blast  furnace 
much  of  the  phosphorus  passes  into  the  iron.  As  far 
as  the  product  of  the  blast  furnace  goes — the  cast  iron 
— the  presence  of  phosphorus  does  no  particular  harm, 
but  as  soon  as  the  cast  iron  has  to  be  converted  into 
steel  it  becomes  highly  objectionable.  With  the  general 
introduction  of  mild  steel,  obtained  cheaply  by  the 
Bessemer  process  of  blowing  air  through  the  molten 
cast  iron  until  all  the  carbon  and  silicon  are  burnt  out  of 
it,  and  then  adding  just  enough  of  an  iron  rich  in  carbon 
to  get  back  to  the  proportion  of  carbon  and  iron  which 
forms  steel,  the  Middlesborough  iron  made  from  the 
Cleveland  ores  was  at  a  serious  disadvantage,  since  it 
contained  a  considerable  amount  of  phosphorus  which 
could  not  be  removed  in  the  Bessemer  process.  After 
much  research  two  chemists,  Thomas  and  Gilchrist, 
invented  a  process  for  removing  the  phosphorus  in  the 
Bessemer  process,  and  so  obtained  a  phosphorus  free 
steel  from  the  impure  Middlesborough  iron.  Their 
plan  was  to  line  the  "  converter,"  the  great  vessel  con- 


128  PHOSPHATIC  MANURES  [chap. 

taining  the  molten  iron  through  which  the  blast  of 
air  was  forced,  with  a  "  basic  "  lining  composed  of  lime 
and  magnesia,  instead  of  the  previous  acid  lining  of 
bricks  composed  mainly  of  silica.  Lime  was  also  added 
to  the  converter,  and  when  the  oxidation  due  to  the 
blast  of  air  takes  place  in  the  molten  metal,  in  presence 
of  the  lime  the  phosphorus  oxidises  as  well  as  the  carbon 
and  silicon,  because  the  resulting  phosphoric  acid  is 
at  once  taken  up  by  the  bases  present  and  so  removed 
from  the  action,  instead  of  being  immediately  reduced 
again  by  the  molten  iron.  Under  these  conditions  the 
resulting  slag,  or  molten  impurities  derived  from  the 
iron,  which  is  "  basic  "  from  the  excess  of  lime  instead 
of  "  acid "  as  usual  from  excess  of  silica,  contains  con- 
siderable quantities  of  phosphoric  acid,  ranging  from 
12  up  to  as  much  as  23  per  cent.  At  the  present  time 
the  Bessemer  has  largely  been  replaced  by  the  "  open 
hearth "  process  of  making  steel,  but  as  the  principle 
is  the  same — the  oxidation  of  the  impurities  in  the 
iron  by  a  current  of  air — it  can  similarly  be  carried 
out  in  the  presence  of  lime  with  the  production  of  a 
"basic  slag"  containing  phosphoric  acid. 

For  some  time  after  Thomas  and  Gilchrist  had  intro- 
duced their  process  in  1879,  ^^o  use  was  made  of  the  basic 
ilag,  though  it  was  known  to  contain  so  much  phosphoric 
acid,  and  it  accumulated  in  the  usual  mounds  near  the 
steel  furnaces.  Various  methods  were  tried  for  extract- 
ing the  phosphoric  acid  or  bringing  it  into  a  soluble 
form,  though  without  any  success ;  but  early  in  the 
'eighties  it  began  to  be  found  that  the  only  thing 
necessary  to  make  the  basic  slag  available  as  a  manure 
was  to  grind  it  to  an  extremely  fine  powder.  In  this 
country  the  value  of  fine  ground  basic  slag  was  first 
brought  to  light  by  Wrightson  and  Munro  in  1885, 
who  carried  out  a  series  of  experiments,  on  a   chalk 


IV.]  BASIC  SLAG  129 

soil  in  Wiltshire  and  a  heavy  clay  in  Durham  with 
basic  slag  finely  ground  on  the  one  hand  and  on  the 
other  dissolved  by  treatment  with  sulphuric  acid,  com- 
pared with  superphosphate  and  other  forms  of  undis- 
solved phosphate.  The  results  were  highly  favourable 
and  showed  that  the  slag  was  comparable  with  super- 
phosphate as  a  source  of  phosphoric  acid  to  the  crop, 
being  much  superior  to  the  other  insoluble  phosphates 
tried.  About  the  same  time  as  Wrightson  and  Munro's 
experiments,  basic  slag,  which  was  known  in  Germany  as 
Thomas  slag  or  Thomas  phosphate,  after  one  of  the 
inventors,  attracted  considerable  attention  there ;  many 
experiments  were  made  with  it  and  turned  out  so  success- 
ful that  it  rapidly  grew  into  considerable  demand  for 
agricultural  purposes.  Indeed,  so  much  more  quickly 
was  basic  slag  taken  up  in  Germany,  that  a  considerable 
export  trade  from  Great  Britain  at  once  grew  up,  and 
even  at  the  present  day  of  the  300,000  tons  annually 
made  in  Great  Britain,  about  150,000  tons  are  exported 
to  Germany. 

Basic  slag,  basic  cinder,  or  Thomas  phosphate 
powder  (the  two  latter  names  are  little  used  in  the 
United  Kingdom  nowadays)  comes  into  the  market 
as  a  dense  black  powder,  so  finely  ground  that  four-fifths 
of  it  will  pass  through  a  fine  brass  wire  sieve  carrying 
100  meshes  to  the  inch,  which  is  found  to  pass  only 
particles  having  a  smaller  diameter  than  0-2  mm.  A 
small  but  varying  amount  of  free  quicklime  is  present ; 
from  2  to  10  per  cent,  may  be  obtained  from  fresh 
samples  by  careful  extraction  with  pure  carbon  dioxide 
free  water.  Both  free  iron  and  magnetic  oxide  of  iron 
are  present,  and  can  be  separated  from  the  bulk  by 
means  of  a  magnet ;  this  test,  together  with  the  presence 
of  free  lime,  the  density  of  the  material,  and  the  evolu- 
tion of  a  little  sulphuretted  hydrogen  on  treatment  with 

I 


130 


PHOSPHATIC  MANURES 


[chap. 


an  acid,  make  it  easy  to  distinguish  between  basic  slag 
and  made-up  imitations  in  which  the  phosphates  are 
derived  from  ground  phosphate  rock. 

Table  XXXIII.  shows  an  analysis  of  the  material, 
in  which  the  most  striking  feature  will  be  seen  to  be 
the  large  amount  of  lime  and  magnesia  present — 
more  than  would  normally  combine  with  the  phos- 
phoric acid,  even  when  allowance  has  been  made  for 
any  lime  that  is  free  or  that  may  be  supposed  to  be 

Table  XXXIII.— Analysis  of  Basic  Slag 
(Stead  and  Ribsdale). 


Lime       ...... 

41.58 

Magnesia 

6'i4 

Alumina 

2-57 

Peroxide  of  Iron 

8-54 

Protoxide  of  Iron    . 

13-62 

„            IVIanganese . 

3-79 

,,           Vanadium 

1.29 

Silica 

7-38 

Sulphur  \ 
Calcium/ 

0-23 

0-3I 

Sulphuric  Anhydride 

0-12 

Phosphoric  Acid     . 

14.36 

99-93 

combined  with  the  silica.  The  analysis  alone  suggests 
that  basic  slag  does  not  contain  the  usual  tri-calcium 
phosphate,  and  its  behaviour  in  the  soil  and  the  ready 
availability  of  the  phosphoric  acid  strengthen  the  view 
that  it  contains  some  other  compound  of  phosphoric 
acid.  For  example,  basic  slag  is  found  to  be  readily 
attacked  by  a  solution  of  carbon  dioxide  or  other  very 
weak  acid  ;  a  much  larger  proportion  of  phosphoric 
acid  goes  into  solution  than  would  be  the  case  with 
an  equally  fine  ground  sample  of  tri-calcium  phosphate 
containing  the  same  amount  of  phosphoric  acid.    Nearly 


1V.5  COMPOSITION  OF  BASIC  SLAG  131 

the  whole  of  the  phosphoric  acid  in  basic  slag  also  goes 
into  solution  when  it  is  shaken  with  an  alkaline  solution 
of  ammonium  citrate,  in  which  tri-calcium  phosphate 
is  not  very  soluble.  The  analysis  of  certain  flat  square 
plate  crystals,  occasionally  found  in  cavities  in  the  balls 
of  slag,  proved  them  to  consist  of  a  tetra-basic  phos- 
phate of  calcium  of  the  formula  (CaO^PgOg,  the  mole- 
cule of  phosphorus  pentoxide  being  combined  with  four 
molecules  of  lime  instead  of  with  three  as  in  ordinary 
calcium  phosphate.  To  this  tetra-basic  phosphate  of 
lime  the  properties  of  basic  slag  have  usually  been 
ascribed,  it  is  supposed  to  be  readily  acted  upon  by 
carbon  dioxide  with  the  formation  of  calcium  carbonate 
and  di-calcium  phosphate,  and  as  this  latter  phosphate 
is  readily  soluble  in  water  containing  carbonic  acid,  the 
availability  of  the  basic  slag  is  accounted  for. 

But  it  is  by  no  means  certain  that  this  association 
of  tetra-calcium  phosphate  with  basic  slag  is  correct. 
In  the  first  place,  the  detailed  analysis  of  the  basic  slag 
hardly  bears  out  this  view ;  there  is  more  lime  than  is 
necessary  to  make  up  tetra-calcium  phosphate  even 
when  every  allowance  is  made  for  silica  and  sulphur, 
and  the  amount  of  free  lime  that  can  be  determined 
is  not  sufficient  to  make  up  the  balance.  Moreover, 
the  crystals  of  tetra-calcic  phosphate  are  only  to  be 
found  in  basic  slags  made  from  irons  poor  in  silicon ; 
the  usual  crystals  found  in  the  basic  slag  cavities  are 
long  hexagonal  needles,  pale  green  or  blue  in  colour, 
of  which  considerable  quantities  can  be  picked  out  from 
the  cindery  portions  of  the  slag.  The  appearance  also 
of  a  fractured  surface  of  the  ordinary  molten  parts  of  the 
slag  would  agree  much  better  with  a  structure  built  up 
of  such  prismatic  crystals  than  of  the  flat  crystals  of  tetra- 
calcium  phosphate.  The  prismatic  crystals,  according  to 
Stead,  consist  of  a  double  silicate  and  phosphate  of  lime 


132  PHOSPHATIC  MANURES  [chap. 

of  the  composition  (CaO)5Po05Si02,  and  contain  about 
29  per  cent,  of  phosphoric  acid,  1 1  per  cent,  of  silica, 
and  56  per  cent,  of  lime.  Moreover,  when  separated 
from  the  mass  of  the  cinder,  finely  ground,  and  attacked 
with  water  charged  with  carbon  dioxide  or  with  very 
dilute  citric  acid,  the  phosphoric  acid  they  contain  shows 
approximately  the  same  solubility  as  that  of  the  phos- 
phoric acid  in  an  ordinary  sample  of  basic  slag,  whereas 
the  crystals  of  tetra-basic  phosphate  of  lime  are  markedly 
less  soluble.  On  the  whole,  it  seems  more  probable  that 
the  typical  phosphoric  acid  compound  of  basic  slag  is 
this  (CaO)5P206Si02 — and  not  the  tetra-calcium  phos- 
phate, (CaO)^?^©^,  especially  as  there  is  plenty  of  other 
evidence  to  show  how  large  a  part  silica  will  play  in 
bringing  phosphoric  acid  into  a  soluble  state. 

Whatever  may  be  the  form  of  combination  of  the 
phosphoric  acid  in  basic  slag,  it  is  undoubtedly  easily 
attackable  by  the  soil  water,  so  that  it  is  more  available 
to  the  plant  than  any  of  the  forms  of  tri-calcium 
phosphate,  though  as  a  rule  it  falls  below  superphos- 
phate. In  this  availability  the  fineness  of  grinding  is 
a  very  important  factor,  and  all  samples  should  be 
carefully  tested  ;  at  least  90  per  cent,  of  the  material 
should  pass  through  the  standard  wire  sieve  of  100 
meshes  to  the  inch.  The  content  in  phosphoric  acid 
varies  with  the  amount  of  phosphorus  present  in  the 
iron  employed  in  the  steel-making  process  ;  of  late  years 
basic  slags  have  been  on  the  whole  richer  than  they 
were  in  the  earlier  years  of  its  manufacture,  and  it  is 
possible  to  obtain  material  containing  23  per  cent,  of 
phosphoric  acid  (equivalent  to  50  per  cent,  of  tri-calcium 
phosphate).  Lower  grade  material  is  more  common, 
but  has  been  shown  to  be  equally  valuable  when 
quantities  containing  equal  amounts  of  phosphoric  acid 
are   compared ;   consequently  basic  slag  should  always 


IV.]  MANUFACTURED  PHOSPHATES  133 

be  bought  on  the  basis  of  an  analysis.  For  a  long  time 
it  was  customary  in  Germany  to  estimate  only  the 
phosphoric  acid  in  the  slag  which  could  be  dissolved 
by  shaking  the  material  for  a  specified  time  with 
an  alkaline  solution  of  ammonium  citrate,  and  to  value 
the  slag  on  such  a  basis,  the  idea  being  that  the  solvent 
differentiated  between  the  available  tetra-calcium  phos- 
phate which  dissolved,  and  other  compounds  of  phos- 
phorus and  phosphoric  acid  with  iron,  which  possessed 
no  fertilising  value  and  did  not  dissolve  in  the  reagent. 
Ammonium  citrate  as  a  solvent  has,  however,  been 
replaced  by  a  2  per  cent  solution  of  citric  acid,  and  in 
the  United  Kingdom  the  vendor  of  basic  slag  is  now 
compelled  to  give  a  guarantee  of  the  percentage  of 
phosphoric  acid  that  is  dissolved  when  5  grms.  of  the 
slag  are  shaken  in  a  litre  bottle  for  half  an  hour  with 
500  c.c.  of  a  solution  containing  10  grms.  of  citric  acid. 
Though  this  method  gives  no  absolute  separation 
between  the  different  phosphates  in  the  slag,  it  affords 
a  sufficiently  good  practical  means  of  estimating  what 
are  easily  soluble  and  therefore  of  fertilising  value. 

A  few  other  manufactured  phosphates  find  their  way 
into  commerce,  though  none  of  them  have  much  agricul- 
tural importance  as  compared  with  superphosphate  and 
basic  slag.  Basic  superphosphate  is  a  form  of  precipi- 
tated calcium  phosphate  introduced  in  1901  by  John 
Hughes  and  made  by  mixing  ordinary  superphosphates 
with  sufficient  lime  to  neutralise  all  the  free  acid  and 
convert  the  superphosphate  into  di-calcium  phosphate, 
leaving  in  addition  a  small  proportion  of  free  lime. 
The  material  is  very  finely  ground  and  forms  a  light 
white  very  bulky  powder,  which  remains  dry  and  works 
readily  through  any  manure-sowing  machine.  On 
analysis  it  shows  a  little  over  12  per  cent,  of  phosphoric 
acid  and  about  4  per  cent,  of  free  lime,  and  as  the  phos- 


134  PHOSPHATIC  MANURES  [chap 

phoric  acid  is  almost  wholly  combined  as  di-calcium 
phosphate,  it  is  to  that  extent  soluble  in  the  dilute  citric 
acid  solution  above  described.  The  fine  state  of  division 
of  this  manure  and  the  form  of  combination  in  which 
the  phosphoric  acid  exists  render  it  very  available  to 
the  plant,  so  that  it  is  a  good  phosphatic  manure  for 
use  on  light  soils  deficient  in  lime,  though  it  may  be 
doubted  whether  a  mode  of  manufacture  which  first 
involves  solution  of  the  phosphoric  acid  by  means  of 
sulphuric  acid  and  then  neutralisation  and  precipitation 
by  lime  is  not  essentially  uneconomical. 

Small  quantities  of  various  forms  of  precipitated 
phosphate  come  on  the  market  from  time  to  time : 
these  are  bye-products  in  the  manufacture  of  gelatine, 
when  the  bones  are  treated  with  hydrochloric  or 
sulphuric  acid  to  dissolve  out  all  the  earthy  matter,  and 
the  resulting  solution  of  phosphoric  acid  is  neutralised 
with  milk  of  lime.  When  the  initial  solution  has  been 
effected  by  sulphuric  acid  the  product  is  sometimes  sold 
as  "phosphatic  gypsum,"  since  it  consists  largely  of 
gypsum  formed  by  the  reaction  of  the  sulphuric  acid 
and  the  lime.  These  fertilisers  are  very  good  sources 
of  phosphoric  acid,  which  is  combined  in  them  in  the 
form  of  di-calcium  phosphate ;  they  form  excellent 
phosphatic  fertilisers  for  light  soils,  being  easily  avail- 
able and  neutral. 

Wiborg  PJwsphate  is  the  product  of  the  heating  of 
apatite,  occurring  as  a  waste  material  mixed  with 
felspar  in  the  preparation  of  certain  Swedish  iron  ores, 
with  sodium  carbonate  in  the  proportions  of  30  soda 
to  100  apatite  containing  17  per  cent,  of  felspar.  The 
result  is  a  phosphate  to  which  Nilson  ascribes  the  formula 
2NaoO.  loCaO.  3P2O5,  which  is  completely  soluble  in 
ammonium  citrate  solution  and  has  proved  to  be 
particularly  valuable  on  the  peaty  soils  poor  in  phos- 


IV.]  MANUFACTURED  PHOSPHATES  135 

phoric  acid  of  the  island  of  Gothland,  though  it  is  not  so 
effective  as  basic  slag  containing  an  equivalent  amount 
of  phosphoric  acid.  While  extensively  used  in  Sweden, 
it  does  not  find  its  way  into  this  country. 

Wolter  Phosphate  is  made  by  melting  together  in  a 
regenerative  furnace  100  parts  of  powdered  phosphorite, 
70  parts  of  acid  sodium  sulphate,  20  parts  of  carbonate 
of  lime,  22  parts  of  sand  and  6  or  7  parts  of  coke,  the 
molten  material  being  run  into  water  and  then  finely 
powdered.  The  resulting  phosphate  is  almost  wholly 
soluble  in  dilute  citric  acid  and  has  proved  in  experi- 
ments to  be  more  assimilable  by  the  plant  than 
phosphoric  acid  in  basic  slag,  and  almost  equivalent 
to  phosphoric  acid  in  superphosphate.  At  present  the 
cheapness  of  basic  slag  and  superphosphate  prevent 
any  wide  distribution  of  fertilisers  of  the  type  of  Wiborg 
and  Wolter  phosphates,  though  they  may  be  remunera- 
tive in  a  locality  where  some  waste  phosphatic  material 
is  available. 


CHAPTER  V 

THE    FUNCTION    AND    USE    OF  PHOSPHATIC 
FERTILISERS 

Ripening  Effect  of  Phosphoric  Acid — Most  manifest  in  wet 
Seasons  —  Effect  of  Phosphoric  Acid  in  stimulating  the 
Formation  of  Roots  and  adventitious  Shoots — Association  of 
Phosphoric  Acid  with  the  Intake  of  Nitrogen  by  the  Plant — 
Solvents  to  determine  the  relative  Availability  of  Phosphatic 
Fertilisers — Relative  Value  of  Phosphatic  Fertilisers  deter- 
mined by  the  Soil — Soils  appropriate  to  Superphosphate — 
Fate  of  Superphosphate  applied  to  the  Soil — Soils  appropriate 
to  Basic  Slag — Neutral  Phosphatic  Manures  for  light  Soils — 
Comparison  of  Bone  Meal  with  other  Phosphatic  Fertilisers. 

Before  considering  the  question  of  the  relative  fertilis- 
ing value  of  the  different  phosphatic  manures  and  their 
application  in  practice,  it  will  be  necessary  to  get  some 
idea  of  the  function  of  phosphoric  acid  in  the  nutrition 
of  the  plant. 

Just  as  nitrogen  delays  maturity  by  promoting 
growth,  phosphoric  acid  has  an  opposite  effect ;  it  is  in 
some  way  closely  bound  up  with  grain  formation,  being 
always  found  in  greater  proportions  in  the  reproductive 
parts  of  the  plant  than  elsewhere.  This  ripening  action 
is  very  clearly  seen  in  the  Rothamsted  experiments  on 
barley ;  the  plots  without  phosphoric  acid  being  as  a 
rule  about  a  week  behind  those  which  receive  this 
fertiliser. 

This  effect  is  brought  out  in  the  diagrams,  Fig.  3, 

136 


80% 


6096 


40% 


20 
2  &4 

2&4 
1&3 
1&3 

July  4 


__j 

• 

,  -'' 

,-''' 

■ TT^) 



/            J 

,-'-'' 

N.        ofwhole 

content  present 

in  the  Grain. 


'  of  Grain 
in  Plant. 


25 


Fig. 


Aug.l 


Curves  showing  the  effect  of  Phosphoric  Acid  in  hastening  the  formation 
of  Grain  of  Barley,  and  the  Migration  of  Nitrogen  to  the  Grain. 
2  and  4  with  Phosphoric  Acid,  i  and  3  without  Phosphoric 
Acid. 


[7'o  jacc  page  137. 


CHAP,  v.]  RIPENING  ACTION  OF  PHOSPHORIC  ACID  137 

which  show  the  results  of  certain  determinations  made 
upon  barley  cut  at  regular  intervals  during  the  develop- 
ment of  the  grain  from  some  of  the  Rothamsted  barley 
plots  in  1904. 

The  two  lower  curves  show  the  rate  of  the  formation 
of  the  grain  week  by  week,  calculated  as  percentages  of 
the  weight  of  the  whole  plant,  for  the  two  plots  which 
receive  phosphoric  acid  and  for  the  corresponding  plots 
without,  both  series  being  similarly  treated  as  regards 
nitrogen  and  potash.  It  will  be  seen  that  the  formation 
of  grain  begins  earlier  where  phosphatic  fertilisers  have 
been  used,  and  even  at  the  end  is  more  complete. 
Similarly,  the  two  upper  curves  show  the  migration  of 
the  nitrogen  to  the  grain,  again  calculated  as  percent- 
ages of  the  nitrogen  of  the  whole  plant,  and,  as  before, 
the  movement  of  nitrogen  begins  at  an  earlier  date,  and 
is  more  completely  carried  out  when  there  is  plenty  of 
phosphoric  acid. 

Table  XXXIV.— Effect  of  Phosphoric  Acid  and  Potash  upon 
Barley  at  Rothamsted.    Wet  and  Dry  Year  compared. 


Grain, 
Bushel3. 

Grain  to 
100  Straw. 

Nitrogen 
per  cent. 
in  Grain. 

1893. 

1894. 

1893. 

1894. 

1893. 

1894. 

Ammonium  Salts  alone     . 

Ammonium  Salts  and 
Superphosphate     . 

Ammonium  Salts  and 
Potash  .... 

Ammonium  Salts,  Super- 
phosphate, and  Potash  . 

II.6 
I8-I 
16.8 
30-8 

10-4 

34-9 
17-8 
41-4 

85-3 

lOI-O 

S5-9 

102-2 

67-5 
77-0 
73-8 
77-7 

2-19 
2-13 
2-17 

2-08 

1-65 
I '60 
I -61 
1-44 

As  might  be  expected,  this  ripening  effect  of  phos- 
phoric acid  will  be  particularly  seen  in  a  wet  year  when 
the  crop  is  late  to  harvest.  Table  XXXIV.  will  illus- 
trate the  point :  it  gives  the  yield  and  other  particulars 


138 


PHOSPHATIC  FERTILISERS 


[chap. 


of  one  series  of  the  Rothamsted  barley  plots  in  1893,  a 
specially  dry  season,  and  in  1894,  vvhich  was  almost 
equally  wet. 

The  phosphoric  acid  increases  the  proportion  of  grain 
to  straw,  and  decreases  the  nitrogen  content  of  the  grain, 
and  it  will  be  noticed  that  this  latter  effect  is  more 
marked  in  the  wet  season  of  1894.  Even  on  the  yield 
itself  the  phosphoric  acid  had  the  greater  effect  in  the 
wet  season. 

Exactly  the  same  result  can  be  observed  in  the 
wheat  crop,  as  may  be  seen  in  Table  XXXV.,  which 
gives  the  yield  of  grain  and  straw  in  1879,  the  wettest 
year  in  the  Rothamsted  records,  and  in  1893,  which  was 
characterised  by  an  extremely  dry  hot  spring  and 
summer. 


Table  XXXV.— Effect  of  Phosphoric  Acid  and  Potash  on  the 
Development  of  Wheat.    Bkoadbalk  Field,  Rothamsted. 


Grain, 
Bushels. 

Straw, 
Cwts. 

Weight  per 
Bushel,  lb. 

Grain  to 
100  Straw. 

WET  SEASO^ 

r,  1879. 

Unmanured        .         .         . 
Nitrogen  only    . 
Nitrogen  and  PgOg    . 
Nitrogen,  PaOg,  and  KgO  . 

4-5 

4-3 

ii-i 

16.0 

6.7 

8.5 

i8.o 

27.2 

51-8 
50-8 

54-6 
57-8 

42-8 
33-6 

36-2 
35-2 

DRY    SEASON 

,    1S93. 

Uiinmnured        .         ,         . 
Nitrogen  only   .         .         . 
Nitrogen  and  PgOg    . 
Nitrogen,  PgOg,  and  K„0  . 

10.7 

8.4 

7*7 
1 5-4 

5-6 
5-6 
6.2 
9-7 

62.5 
59-1 
56-4 
62.6 

II 0-3 
84-4 
67-3 
98-0 

In  the  wet  year  the  use  of  phosphoric  acid  in- 
creases the  yield  from  4-3  bushels  with  nitrogen  only 
to  IM  bushels  with  nitrogen  and  phosphoric  acid,  the 


v.]       ■  ACTION  OF  PHOSPHORIC  ACID  139 

proportion  of  grain  to  straw  being  raised  from  33  6  to 
36-2.  In  the  dry  year  the  phosphoric  acid  so  hurried 
on  the  premature  ripening  of  the  grain  that  the  yield 
declined  from  8-4  to  y-y  bushels,  and  the  proportion  the 
grain  bore  to  the  straw  similarly  fell  from  84-4  to  67-3 
per  100  of  straw. 

The  action  of  phosphoric  acid  on  the  plant  is  not 
confined  to  its  ripening  effect ;  it  stimulates  the  early 
development  of  the  young  seedling  to  a  remarkable 
extent.  Farmers  are  well  acquainted  with  the  good 
start  that  any  crop  gets  when  manured  with  super- 
phosphate ;  indeed,  it  is  often  used  merely  to  secure  a 
better  plant,  though  with  little  expectation  of  otherwise 
increasing  the  yield.  More  than  sixty  years  ago  this 
had  been  noticed  by  the  late  Sir  John  Lawes ;  and  in 
one  of  his  earliest  papers  on  "  Turnip  Culture  "  in  1847, 
he  writes  :  "  Whether  or  not  superphosphate  of  lime  owes 
much  of  its  effect  to  its  chemical  actions  in  the  soil,  it  is 
certainly  true  that  it  causes  a  much  enhanced  develop- 
ment of  the  underground  collective  apparatus  of  the 
plant,  especially  of  lateral  and  fibrous  root."  For  this 
statement  he  was  vigorously  attacked  by  Liebig,  but 
some  experiments,  which  are  still  in  progress,  show  that  it 
was  the  result  of  sound  observation  and  that  in  some 
way  or  other  phosphoric  acid  does  stimulate  the  root 
development  of  the  young  plant  Barley  seedlings,  for 
example,  grown  in  water  cultures  without,  or  with  a 
minimal  amount  of,  phosphoric  acid  develop  practically 
no  root,  whereas  when  they  are  nitrogen  or  potash 
starved  the  root  growth  will  be  proportional  to  that 
of  the  rest  of  the  plant.  Both  in  the  field  and  in 
pot  experiments  the  phosphoric  acid  has  a  great  effect 
in  promoting  the  formation  of  adventitious  buds, 
so  leading  to  the  tillering  of  the  plant.  To  what 
extent  this  stimulus  to  root  growth  is  brought  about 


I40  PHOSPHATIC  FERTILISERS  [chap. 

by  other  sources  of  phosphoric  acid  and  under  diverse 
conditions  of  soil,  has  not  yet  been  worked  out, 
but  there  can  be  little  doubt  but  that  it  explains  why 
a  phosphatic  manuring  has  such  a  valuable  effect  in 
establishing  the  plant,  even  if  the  gross  yield  is  not 
ultimately  much  enhanced. 

It  may  also  go  to  explain  the  extraordinary  results 
of  quite  small  dressings  of  phosphoric  acid  upon  soils  in 
Southern  Australia,  where  a  manuring  with  half  a 
cwt.  per  acre  or  even  less  of  superphosphate  has  been 
found  sometimes  to  double  the  yield  of  cereals.  On 
analysis  the  soils  are  not  rich,  but  they  show  no  such 
signal  deficiency  in  phosphoric  acid  as  would  account 
for  the  action  of  the  manure ;  it  seems  much  more 
likely  that  in  a  semi-arid  country  where  the  whole 
success  of  the  crop  depends  on  the  roots  getting  quickly 
down  to  the  cooler  and  moister  subsoil,  the  stimulating 
action  of  the  phosphoric  acid  upon  the  young  roots 
becomes  of  the  greatest  value.  In  this  connection  it 
may  be  noted  that  the  two  crops  which  most  respond  to 
phosphatic  manuring,  turnips  and  barley,  are  both 
possessed  of  shallow  roots,  confined  to  a  comparatively 
limited  layer  of  soil ;  whereas,  under  ordinary  farming 
conditions,  wheat  responds  very  little  to  phosphoric  acid 
and  mangolds  hardly  at  all,  both  being  deep-rooted 
plants.  But  even  for  mangolds  farmers  are  accustomed 
to  use  superphosphate,  because  they  have  found  by 
experience  it  is  of  great  assistance  in  securing  a  plant. 

It  has  sometimes  been  stated  that  phosphoric  acid  is 
associated  with  the  assimilation  of  nitrogen  by  the 
plant,  and  particularly  with  its  migration  from  the  stem 
or  roots  into  the  seed,  the  opinion  being  probably 
founded  on  the  fact  that  the  nucleo-proteins,  so  char- 
acteristic of  the  reproductive  parts  of  plants,  contain 
phosphorus.     This  opinion  is  not,  however,  borne  out 


v.]  PHOSPHORIC  ACID  AND  NITROGEN  IN  CROP   141 

by  the  examination  of  a  large  number  of  analyses  of 
barley  grain  from  the  Rothamsted  plots ;  when  phos- 
phoric acid  is  deficient  the  intake  of  nitrogen  is  not 
proportionally  reduced  ;  in  fact,  the  grain  grown  on  the 
plots  receiving  no  phosphoric  acid  is  the  richest  in 
nitrogen. 

This  point  may  be  further  elucidated  from  some 
experiments  upon  wheat  made  at  Rothamsted  in  1907; 
a  large  number  of  ears  of  wheat  were  marked  just  as 
they  came  into  flower,  in  order  to  secure  that  all  should 
be  as  nearly  as  possible  the  same  age  at  starting.  A 
number  of  these  heads  were  gathered  every  third  day, 
and  the  grain  was  extracted  and  analysed,  so  as  to  trace 
any  progressive  changes  in  composition  as  the  grain 
formed  and  ripened.  Table  XXXVI.  shows  the  ratio 
of  nitrogen  to  phosphoric  acid  in  such  grain  from  three 
of  the  Rothamsted  plots — from  the  unmanured  Plot  3, 
where  all  the  elements  of  nutrition  and  particularly  nitro- 
gen are  lacking  ;  from  Plot  10,  where  there  is  an  excess 
of  nitrogen  and  a  great  deficiency  of  phosphoric  acid ; 
and  from  an  adjoining  plot  under  ordinary  farming 
conditions,  where  phosphoric  acid  will  be  relatively 
abundant.  It  will  be  seen  that  on  any  plot  the  ratio 
of  nitrogen  to  phosphoric  acid  remains  pretty  constant 
throughout  the  whole  development  of  the  grain,  but 
that  a  different  ratio  exists  for  each  plot.  From  this 
we  may  conclude  that  the  material  which  the  plant  on 
any  particular  plot  moves  from  its  straw  and  root  to 
form  into  grain  is  the  same  throughout  the  development 
of  the  grain,  but  that  each  plant,  according  to  the  soil 
and  manure  conditions  under  which  it  is  growing, 
builds  up  a  type  of  grain  of  a  composition  special  to 
itself  It  is  true  that  the  nitrogen  and  phosphoric  acid 
move  into  the  grain  pari  passu,  and  in  that  sense  the 
phosphoric  acid  might  be  regarded  as  a  carrier  of  the 


142 


PHOSPHATIC  FERTILISERS 


[chap. 


nitrogen,  but  then  the  starch  also  migrates  in  an  equally 
constant  ratio  to  the  nitrogen  compounds,  though  no 
such  association  is  claimed  between  nitrogen  and  starch. 
Both  actually  and  relatively  the  nitrogen  is  highest  in 
the  grain  from  Plot  lo,  where  the  plant  is  phosphoric 
acid  starved. 

Table  XXXVI.— Development  of  Wheat  Grain,  1907. 


Date. 

Plot  3. 

Ui)  manured. 

Plot  ao. 

Nitrogen  only. 

Normal 
Manuring. 

Nitrogen 

per  cent. 

in  Dry 

Grain. 

Ratio  of 
Nitrogen 
to  P2O5. 

Nitrogen 

per  cent. 

in  Dry 

Grain. 

Ratio  of 
Nitrogen 
to  P2O5. 

Nitrogen 

per  cent. 

in  Dry 

Grain. 

Ratio  of 

Nitrogen 
to  P2O5. 

July   16    . 
„      19    . 

„       22      . 
.,       25      . 
„       28      . 
„       31      • 

Aug.    3    . 
,,       6    . 

„       9    . 
„     12    . 

.,     15    . 
„     18    . 
1.     21    . 
„     24    . 
„     27    . 
„     30    . 

2.68 
2-41 
2.46 
2-17 
2-12 
2 -06 

1.86 

1.83 

1.80 
1.72 

1-86 
1-79 
1-85 
1.78 

2-15 
2-15 

2-12 
2.00 
2.05 
2-22 
1.87 
2-04 
1.89 

1-86 
2.28 
1.96 
2.06 
1.99 

2-6l 

2-45 

2-13 
2-IO 
2.1 1 
1-92 

1-85 
I-S8 
1-83 
1-83 
1-88 
1.90 

... 

2-35 

2-32 
2-25 

2-53 

2-32 
2-27 
2-50 

2-45 
2-41 
2.17 
2-29 
2.38 

2-27 
2-20 
2-05 
1-97 
1-84 
1.35 
1-89 
1-88 
2.03 
1.98 
2-05 

I-9I 
1-88 
1-91 
1.85 
1.82 

2-00 
I.8I 
1.82 
I.9I 
1.85 
1-98 

The  phosphatic  manures  are  practically  all  com- 
pounds of  phosphoric  acid  with  lime,  and,  as  is  well 
known,  four  distinct  combinations  exist  and  are  found 
in  commerce.  Only  one,  the  dihydrogen  calcium 
phosphate,  the  characteristic  constituent  of  super- 
phosphate, is  to  any  degree  soluble  in  water;  the 
others  give  rise  to  extremely  dilute  solutions  of  phos- 
phoric acid,  too  dilute,  as  has  been  shown  by  experiment 
to  nourish  a  plant  properly,  with  however  large  a  volume 


v.]  SOLUBTTJTY  OF  PHOSPHATES  143 

of  the  solution  it  may  be  in  contact.  Yet  insoluble  as  di-, 
tri-,  and  tetra-basic  phosphate  of  lime  are,  when  they  are 
sufficiently  finely  divided  and  well  incorporated  with  the 
soil  so  as  to  be  in  contact  with  the  roots,  they  are  all 
effective  in  supplying  the  plant  with  phosphoric  acid. 
It  will  be  shown  later  (p.  290)  that  the  carbonic  acid 
excreted  by  the  roots  of  the  plants  is  the  chief  agent 
in  producing  a  solution  in  the  soil  water  capable  of 
attacking  these  insoluble  phosphates  ;  acid  humus  and 
ammonium  sulphate,  which  gives  rise  to  free  acid  in 
soils,  also  assist  in  rendering  them  available  to  the 
plant. 

Since  only  one  of  the  commercial  phosphates  is 
freely  soluble  in  water,  yet  all  of  them  have  to  enter 
into  solution  before  they  can  be  utilised  by  the  plant, 
the  question  of  their  relative  availability  is  not  easy  to 
settle,  and  a  variety  of  solvents  have  been  proposed  for 
its  determination  in  the  laboratory.  In  Germany,  for 
example,  basic  slag  was  formerly  valued,  not  on  the  total 
amount  of  phosphoric  acid  it  contains,  but  on  the 
amount  that  is  soluble  in  a  strong  ammoniacal  solution 
of  ammonium  citrate,  the  idea  being  that  this  reagent 
discriminates  between  the  tri-calcium  phosphate,  which 
is  insoluble,  and  the  di-  and  tetra-calcium  phosphates, 
which  will  dissolve  in  the  medium.  Instead  of  the 
ammonium  citrate,  a  2  per  cent,  solution  of  citric  acid 
is  now  employed,  and  i  per  cent,  and  o-i  per  cent. 
solutions  have  also  been  proposed  by  various  chemists 
for  the  valuation  of  phosphatic  fertilisers.  None  of 
these  solvents,  however,  really  draws  a  sharp  distinc- 
tion between  the  different  phosphates,  which  are  all 
soluble  up  to  a  certain  point,  when  an  equilibrium  is 
established  between  the  phosphoric  acid  in  solution  and 
that  remaining  undissolved.  If  the  first  solution  formed 
is   replaced   by  a  fresh  portion   of  the   solvent,   more 


144 


PHOSPHATIC  FERTILISERS 


[chap. 


phosphoric  acid  will  come  into  solution  ;  in  fact,  all  the 
phosphates  can  be  eventually  completely  dissolved 
away  by  the  solvents  in  question.  The  following  table 
(XXXVII.)  shows  the  amount  of  phosphoric  acid 
extracted  by  a  i  per  cent,  solution  of  citric  acid  from 
one  of  the  Broadbalk  soils  manured  for  fifty  years  with 
superphosphate,  the  extraction  being  repeated  with  fresh 
solvent  as  soon  as  one  portion  had  been  saturated  and 
then  removed : — 

Table  XXXVII.— ioo  Grms.  Broadbalk  Soil  (Plot  7),  with 
I  Litre  i  per  cent.  Solution  of  Citric  Acid. 


First  Extraction 

56'i  mg.  PgOj  dissolved 

Second         ,, 

22-8         „                 „ 

Third           „ 

8-9         ,, 

Fourth         „ 

6-5        „ 

Fifth            „ 

4-4        »                ,, 

Sixth            „ 

4-4        „                » 

Very  similar  results  have  been  obtained  when 
manures  are  treated  in  the  same  manner,  and  they 
may  be  taken  to  show  that  a  single  extraction  of  any 
solvent  of  the  kind  proposed  does  not  dissolve  the 
whole  of  a  particular  compound  of  phosphoric  acid, 
which  may  be  thereupon  reckoned  as  distinct  in  kind 
from  the  rest  of  the  phosphates  left  unattacked.  This 
mode  of  attack  with  weak  solvents  should  be  regarded 
as  affording  only  empirical  figures  to  assist  the  analyst 
in  forming  a  judgment  of  the  manure;  and  the  condi- 
tions of  making  the  solution,  such  as  time,  shaking, 
relative  amounts  of  solvent  and  substance,  must  be 
strictly  defined.  Furthermore,  the  only  solvent  which 
has  any  a  priori  justification  is  a  solution  of  carbon 
dioxide,  such  as  does  the  work  in  the  soil ;  the  acids  of 
the  cell  sap,  to  resemble  which  citric  acid  was  taken, 
have  been  shown  to  experience  no  direct  contact  with 
the  soil  particles. 


v.] 


SOLUBILITY  OF  PHOSPHATES 


145 


The  kind  of  information  which  is  yielded  by  the 
attack  of  dilute  solvents  may  be  seen  in  Table  XXXVIIL, 
which  shows  some  of  the  results  obtained  by  J.  K.  S. 
Dixon  when  certain  phosphates  of  similar  character 
were  shaken  with  a  2  per  cent,  solution  of  citric  acid. 
The  results  agree  in  the  main  with  practical  experience 
and  with  the  field  trials  which  have  been  made  upon 

Table  XXXVIIL — Relative  Solubility  of  various 
Phosphatic  Manures  (Dixon). 


PoOs  dissolved 

by  2  per  cent. 

Manure. 

Nitrogen. 

Total  P2O6. 

Citric  Acid 
Solution  as 
per  cent,  of 
total  P2O5. 

Per  cent. 

Per  cent. 

Steamed  Bone  Meal 

1-86 

29-07 

64-29 

Steamed  Bone  Flour         . 

1.07 

29-14 

70-55 

English  Bone  Meal  . 

5-17 

22-46 

56-67 

Indian        „         »      •         <        • 

3-35 

23-19 

52-29 

Peruvian  Guano       .         . 

1-40 

27-28 

66-05 

)>            )>            ♦         .        » 

3-26 

21-36 

85-95 

))            »t            ... 

8.II 

13-13 

95-73 

these  materials  ;  the  phosphoric  acid  of  bone  meal  is  less 
soluble  than  that  of  steamed  bone  flour,  and  the  Indian 
bones  which  have  long  been  dried  and  exposed  show  a 
lower  solubility  than  do  the  fresh  English  bones.  The 
phosphatic  guano  and  the  steamed  bone  flour  show 
much  the  same  solubility  of  their  phosphoric  acid,  but 
the  younger  the  guano  is,  as  indicated  by  the  increased 
percentage  of  nitrogen,  the  greater  is  the  solubility  of 
the  contained  phosphoric  acid.  It  will  be  explained 
later  that  as  the  guano  ages  and  loses  its  nitrogen  the 
phosphates  pass  more  and  more  into  tri-calcium  phos- 
phate, and  eventually  by  solution  and  redeposition 
become  much  the  same  material  as  a  rock  phosphate. 
But  while  it  would  thus  be  possible  by  the  use  of  one 

K 


146  PHOSPHATIC  FERTILISERS  [cHAP. 

of  these  weak  acid  solvents  to  arrange  the  various 
phosphates  in  a  scale  of  decreasing  solubility,  and  argue 
from  that  as  to  their  availability  to  the  plant,  the  order 
of  the  table  would  not  represent  their  relative  value  in 
practice. 

In  considering  the  action  of  the  various  phosphatic 
manures  in  the  field,  the  most  important  factor  to  be 
taken  into  account  is  the  soil,  for  the  relative  value  of 
the  fertilisers  will  change  entirely  with  different  types 
of  soil.  For  example,  the  choice  between  super- 
phosphate and  basic  slag  or  bone  meal,  as  a  phos- 
phatic manure,  must  be  determined,  not  by  their 
comparative  solubility,  but  by  the  amount  of  calcium 
carbonate  and  the  wetness  or  dryness  of  the  soil  to 
which  the  fertiliser  is  to  be  applied.  A  very  large 
number  of  experiments  have  been  made  to  institute 
a  comparison  between  these  fertilisers,  but  without 
resulting  in  any  very  general  information,  just  because 
the  question  is  really  settled  by  those  external  soil 
factors  which  are  generally  unrecorded.  On  certain 
soils  one  or  other  of  these  manures  will  always  give 
the  best  results,  on  other  soils  their  effects  may  be  so 
much  alike  that  the  choice  between  them  can  be 
settled  by  price  alone  or  by  any  consideration  of 
convenience  that  may  enter.  For  example,  in  one 
of  the  Rothamsted  experiments  one  series  of  plots 
receive  superphosphate,  another  series  basic  slag,  and 
a  third  bone  meal,  in  quantities  supplying  the  same 
phosphoric  acid  to  each,  the  plots  being  otherwise 
treated  alike  as  regards  nitrogen  and  potash.  If  we 
abstract  the  results  which  refer  to  the  yields  in  the 
year  of  the  application  of  each  manure  and  reduce 
them  to  a  common  standard  each  year  by  taking  the 
yields  of  the  unmanured  plot  as  loo,  we  obtain  the 
relat've  figures  in  Table  XXXIX. 


v.]  RELATIVE  VALUE  OF  VARIOUS  PHOSPHATES  147 


It  will  be  seen  that  the  phosphates  have  produced  a 
greater  effect  upon  Swedes  and  barley  than  upon  the 
deeper  rooting  and  more  slowly  growing  mangolds  and 
wheat,  but  that  on  the  whole  the  three  fertilisers  are 
equally  valuable  as  sources  of  phosphoric  acid  on  the 
Rothamsted  soil.  The  soil  of  the  Little  Hoos  field,  in 
which  the  experiment  is  being  conducted,  contains  a 

Table  XXXIX.— Relative  Yield  from  various  Phosphates 
(Rothamsted).     Unmanured  =  100. 


Crop. 

Superphosphate. 

Basic  Slag. 

Bone  Meal. 

! 

Swedes       . 
Barley        .         . 

Mangolds  . 

Wheat 

Swedes 

120 
119 
114 
106 
132 

1X6 
121 
105 
108 
109 

126 

no 

III 
117 
131 

Means  . 

118 

112 

119 

reasonable  working  quantity  of  carbonate  of  lime;  it 
is  also  fairly  heavy  and  cool,  so  that  it  retains  sufficient 
moisture  to  give  the  phosphates  of  basic  slag  and  bone 
meal  an  opportunity  of  coming  into  solution. 

Without  attempting  any  detailed  review  of  the 
numerous  experiments  upon  phosphatic  fertilisers,  we 
may  yet  draw  certain  general  conclusions  from  them. 

On  nearly  all  normal  soils  superphosphate  is  the 
most  effective  phosphatic  fertiliser  when  equal  amounts 
of  phosphoric  acid  are  compared.  The  exceptions  are 
the  light  sands  and  gravels  very  deficient  in  carbonate 
of  lime,  peaty  soils  where  the  humus  is  of  the  sour  acid 
type  and  all  other  soils  that  have  developed  an  acid 
reaction.  On  the  peaty  soils  of  the  fen  country 
superphosphate  is  the  fertiliser  most  valued,  but 
there  the   humus   is   of    the   "  mild "   type,   consisting 


148  PHOSPHATIC  FERTILISERS  [chap. 

of  calcium  humate,  with  which  the  superphosphate 
reacts. 

When  superphosphate  is  applied  to  the  soil,  the 
soluble  phosphoric  acid  it  contains  is  rapidly  repre- 
cipitated ;  to  some  extent  the  clay  provides  the 
necessary  base,  but  on  most  soils  the  calcium  carbonate 
takes  the  chief  part  in  the  reaction,  with  the  pro- 
duction of  di-calcium  phosphate.  As  this  precipita- 
tion takes  place  all  throughout  the  soil,  the  phosphate 
is  very  finely  divided  and  thoroughly  disseminated, 
hence  the  great  effectiveness  of  superphosphate. 
Though  di-calcium  phosphate,  like  tri-calcium  phos- 
phate itself,  is  probably  eventually  converted  in  the  soil 
into  a  compound  approaching  the  composition  of  tetra- 
calcium  phosphate,  it  remains  effective  as  a  fertiliser 
because  of  the  fine  state  of  division  in  which  it 
continues  to  exist. 

How  thorough  is  the  precipitation  of  the  phos- 
phoric acid  within  the  soil  may  be  seen  from  Dyer's 
examination  of  the  soils  from  the  Broadbalk  wheat 
field,  which  had  been  receiving  3I  cwts.  per  acre  of 
high  grade  super  for  fifty  years  previously.  He  found 
that  though  the  surface  soil  to  the  depth  of  9  inches 
had  been  enormously  enriched  in  phosphoric  acid 
soluble  in  i  per  cent,  solution  of  citric  acid,  the  subsoil 
below  had  practically  gained  none,  so  complete  had  been 
the  precipitation  in  the  layer  stirred  by  the  plough. 
Again,  the  drainage  waters  from  these  plots  show  a 
most  trifling  amount  of  phosphoric  acid,  so  that  losses 
by  washing  out  must  be  negligible.  Still  more  cogent 
evidence  of  the  retention  of  phosphoric  acid  by  the  soil 
has  been  obtained  more  recently  by  applying  the  method 
of  successive  extractions  with  a  i  per  cent  solution  of 
citric  acid,  until  the  phosphoric  acid  going  into  solution 
has   fallen   to   the   low   constant  figure   indicating  the 


V.J  RETENTION  OF  PHOSPHORIC  ACID  BY  SOIL    149 


solubility,  not  of  the  recently  added,  but  of  the  original 
soil  phosphates.  About  five  extractions  remove  the 
phosphoric  acid  down  to  this  point,  further  extractions 
remove  very  little  more,  and  the  sum  of  the  phosphoric 
acid  dissolved  in  these  five  extractions  approximates 
very  closely  to  the  surplus  of  phosphoric  acid  supplied 
as  superphosphate  over  that  removed  in  the  crop. 

Table  XL.— Phosphoric  Acid  soluble  in  Five  Extractions  with 
I  PER  cent.  Citric  Acid,  compared  with  that  in  Manure 
AND  Crop  (Rothamsted). 


Phosphoric  Acid,  lb.  per  acre. 

Supplied  in 
Manure. 

Kemoved  in 

Crop. 

Surplus  in 
Sou. 

Dissolved  by 
1  per  cent. 
Citric  Acid. 

Broadbalk,  Plot  3    • 
..    5    • 
11            II     7    • 
„    8    , 
Hoos,  Plot  I    . 
,-     2   . 
..        „     4   . 

3960 
3810 
3810 

3390 
3390 

550 

790 

1370 

1520 

555 
1200 
1240 

-550 
3170 
2440 
2290 

-555 
2190 
2150 

565 
3000 

2470 

2055 
400 

2315 
2000 

This  shows  that  phosphoric  acid  supplied  as  super- 
phosphate remains  in  the  surface  soil,  and  in  a  form 
that  is  readily  soluble  in  such  weak  acids  as  a  dilute 
solution  of  citric  acid  or  the  natural  solution  of  carbon 
dioxide  occurring  in  the  soil.  Doubtless  the  result 
would  be  modified  if  the  soil  were  not  well  provided 
with  calcium  carbonate,  in  which  case  more  insoluble 
phosphates  of  iron  and  alumina  would  be  formed.  It 
is  a  fair  conclusion  to  draw  from  these  results  that 
superphosphate  and  indeed  all  phosphatic  manures, 
may  be  applied  to  the  land  much  earlier  than  is  usually 
the  case ;  because  there  is  not  the  least  fear  of  their 
washing  out,  and  it  is  all-important  to  get  them   well 


ISO  PHOSPHATIC  FERTILISERS  [chap. 

disseminated  through  the  soil.  For  the  turnip  crop  there 
may  perhaps  be  some  advantage  in  drilling  the  manure 
with  the  seed,  so  important  is  it  to  have  the  young 
roots  stimulated  by  an  abundance  of  phosphoric  acid 
close  at  hand,  but  with  other  crops  much  of  the  benefit 
of  phosphatic  manures  is  often  lost  because  they  are 
applied  when  the  land  has  already  begun  to  run  short  of 
water.  Fine  grinding  and  early  application  are  the  two 
great  factors  in  making  phosphatic  manures  available. 

The  essential  condition  that  should  dictate  the  choice 
of  superphosphate  as  a  fertiliser,  is  the  presence  of 
sufficient  carbonate  of  lime  in  the  soil  to  ensure  the 
precipitation  of  the  soluble  phosphoric  acid  as  a  calcium 
compound.  On  acid  soils,  on  some  clays,  and  on  many 
sands  and  gravels,  there  is  such  a  deficiency  of  carbonate 
of  lime  that  the  phosphoric  acid  becomes  precipitated 
as  iron  or  aluminium  phosphate,  which  possess  a  much 
lower  solubility  in  the  soil  water  and  are  therefore 
less  available  to  the  plant.  But  on  the  great  majority 
of  our  British  soils  experience  has  shown  that  the 
extra  price  of  the  unit  of  phosphoric  acid  in  its  soluble 
form  in  superphosphate  is  more  than  justified  by  its 
superior  effectiveness,  which  is  due  to  the  rapidity  with 
which  it  becomes  disseminated  in  a  finely  divided 
condition  in  the  soil  immediately  near  the  roots  of  the 
crop. 

On  many  of  the  heavier  clays,  which  are  in  general 
deficient  in  phosphates,  though  superphosphate  is  a 
valuable  fertiliser,  especially  if  lime  has  been  applied  to 
the  soil  previously,  basic  slag  is  really  the  more  effective 
manure  when  quantities  costing  the  same  money  are 
compared.  In  the  first  place,  basic  slag  is  so  much 
cheaper  that  nearly  twice  as  much  phosphoric  acid  can 
be  bought  at  the  same  cost,  and  on  heavy  soils  well 
provided  with  moisture  or  on  peaty  soils  its  effectiveness, 


v.]         PHOSPHATES  APPROPRIATE  TO  SOILS        151 

unit  for  unit,  is  not  much  less  than  that  of  the  phos- 
phoric acid  in  superphosphate,  especially  when  it  has 
been  put  on  early  and  has  had  plenty  of  time  to 
saturate  the  soil  water  and  to  be  disseminated  within 
the  soil  by  solution  and  reprecipitation. 

Moreover,  the  lime  contained  in  the  basic  slag  is 
itself  of  considerable  value ;  it  supplies  what  is  often  a 
much-needed  base,  and  on  old  grass  land  in  particular 
its  effect  in  bringing  the  soil  potash  into  solution  and 
in  promoting  the  oxidation  of  the  nitrogenous  reserves 
in  the  soil  is  very  marked ;  on  tillage  land  also  the 
lime  is  of  assistance  in  improving  the  texture  of  the 
soil.  When  such  soils  are  poor  in  carbonate  of 
lime  there  is  always  some  danger  of  "finger-and-toe" 
in  the  turnips,  and  if  once  this  disease  has  appeared 
superphosphate  should  no  longer  be  used,  but  basic 
slag  should  take  its  place.  The  spread  of  the  disease 
is  promoted  by  any  acid  manure  like  superphosphate ; 
the  free  lime  of  basic  slag,  on  the  contrary,  tends  to 
render  the  soil  unfit  for  the  survival  of  the  spores.  Thus 
the  choice  between  superphosphate  and  basic  slag 
should  in  the  main  be  determined  by  the  soil ;  the 
more  calcareous  and  loamy  the  soil,  the  more  effective 
is  superphosphate,  but  heavy  soils  and  land  poor  in 
carbonate  of  lime  respond  better  to  basic  slag,  and  on 
wet  sour  soils  no  other  phosphatic  manure  should 
be  used. 

In  this  country  there  is  rather  a  prejudice  against 
the  use  of  basic  slag  on  the  lighter  soils — the  sands,  and 
gravels,  which  are  yet  too  poor  in  carbonate  of  lime  to 
be  fitted  for  superphosphate.  They  are  generally 
regarded  as  too  dry  to  allow  the  basic  slag  to  be  effec- 
tive, but  in  view  of  the  value  that  basic  slag  has  been 
found  to  possess  on  the  light  sandy  soils  of  Eastern 
Germany,  where,  too,   the   rainfall  is  less  than  that  of 


152  PHOSPHATIC  FERTILISERS  [chap. 

England,  the  popular  opinion  seems  to  be  founded  on 
a  misapprehension.  It  has  probably  arisen  from  the 
fact  that  on  the  poor  sandy  grass  pastures  basic  slag 
never  shows  the  extraordinary  effect  it  does  on  the 
poor  clay  pastures.  This  is  due,  not  to  the  ineffective- 
ness of  the  phosphoric  acid  in  the  basic  slag,  but  to  the 
lack  in  the  sandy  soil  of  both  potash  and  of  humus  to  be 
set  in  action  by  the  lime  contributed  by  the  basic  slag. 
The  great  outburst  of  white  clover  which  often  follows 
the  application  of  basic  slag  to  a  clay  pasture  is 
mainly  promoted  by  the  potash  liberated  from  the  soil. 
As  a  source  of  phosphoric  acid  for  tillage  land  basic 
slag  is  probably  little  less  effective  on  a  light  than  a 
heavy  soil,  but  it  should  be  applied  early  and  well 
worked  in. 

On  such  light  land,  however,  there  is  a  very  general 
preference  for  some  of  the  forms  of  insoluble  phosphate 
that  are  found  by  experience  to  be  readily  attacked 
by  the  soil  water  and  available  to  the  plant ;  phosphatic 
guano,  steamed  bone  flour,  basic  superphosphate,  and 
precipitated  phosphate  are  all  of  the  type  that  is  valu- 
able on  such  soils.  Very  effective  phosphatic  fertilisers 
for  light  soils  deficient  in  carbonate  of  lime,  and  there- 
fore requiring  a  neutral  manure,  may  be  made  by  mix- 
ing about  two  parts  of  superphosphate  with  one  of 
steamed  bone  flour,  phosphatic  guano,  bone  meal,  or 
basic  slag  itself.  If  the  mixture  be  left  in  a  heap  for  a 
time  in  the  manure  shed  the  superphosphate  will  react 
with  the  tri-calcium  phosphate  of  the  bone  or  guano 
to  produce  a  di-calcium  or  precipitated  phosphate  ;  and 
though  the  mass  cakes  a  little  when  the  reaction  is 
complete,  it  can  easily  be  broken  down  into  the  original 
fine  powder.  This  is  probably  the  cheapest  way  of 
obtaining  an  easily  available  neutral  phosphate  for  use 
on  light  arable  land  where  superphosphate  is  unsuitable 


v.] 


BONE  MEAL 


153 


because  of  the  lack  of  carbonate  of  lime.  Otherwise 
the  choice  between  these  different  phosphates  is  very 
much  one  of  price,  since,  phosphoric  acid  for  phosphoric 
acid,  they  have  proved  to  be  about  equally  effective. 

Raw  bones  or  bone  meal,  though  the  price  has  been 
at  a  low  level  for  some  years,  still  seems  to  be  rated  too 
highly,  the  nitrogen  of  the  phosphoric  acid  it  contains 
being  over-valued  if  we  take  into  account  the  low 
availability  which  field  experiments  indicate  it  possesses. 
Most  of  the  experiments  go  to  show  bone  meal  to  be  so 
slow  in  its  action  that  excessive  amounts  have  to  be 
applied  and  locked  up  in  the  soil  if  any  immediately 
appreciable  result  is  to  be  obtained. 

For  example,  Table  XLI.  shows  the  results  of  one 
series  of  experiments  carried  out  by  the  Highland  and 


Table  XLI.- 


-Returns  from  Bone  Meal  and  other  Phosphatic 
Manures. 


1878. 

1879. 

1880. 

1881. 

Swedes. 

Barley, 

Unmanured. 

Total 

Produce. 

Seeds  Hay, 
Unmanured. 

Oats, 
Manured. 

Total 
Produce. 

Ground  Coprolites  . 
Bone  Meal 
Phosphatic  Guano  . 
jround    Coprolites, 

dissolved 
Bone  Meal,  dissolved 
No  Phosphate 

Tons. 
150 
13-4 
15.4 

15-8 
I3-I 

Lb. 

5844 
6052 
6016 

5964 
6364 
5955 

Cwts. 
38.5 
41-5 
33'8 

41-3 
44-3 
33*5 

Lb. 

5911 
66S6 
6726 

7696 
7460 
7132 

Agricultural  Society,  wherein  bone  meal  was  less 
effective  than  fertilisers  of  the  superphosphate  class, 
not  only  in  the  year  of  its  application  but  afterwards 
also,  when  further  crops  were  grown  without  the 
application  of  fresh  manure.     It  is  probably  on  grass 


rS4  PHOSPHATIC  FERTILISERS  [chap. 

land  that  bone  meal  answers  best,  for  there  the  fine 
roots  of  the  grasses  can  come  into  very  intimate  contact 
with  the  fragments  of  the  fertiliser. 

The  reason  of  the  comparative  ineffectiveness  of 
bone  meal  is  not  far  to  seek :  owing  to  the  toughness 
of  the  cartilage  structure  of  the  bone,  it  is  a  matter  of 
difficulty  to  reduce  it  to  a  really  fine  state  of  division 
— at  any  rate  the  bone  meal  of  commerce  is  a  com- 
paratively coarse  powder.  Now,  it  has  already  been 
pointed  out  that  a  tri-calcic  phosphate,  such  as  exists  in 
bones,  is  very  far  from  insoluble  in  water  charged  with 
carbon  dioxide,  but,  as  with  all  sparingly  soluble  salts, 
the  rate  of  solution  will  be  proportional,  other  things 
being  equal,  to  the  amount  of  surface  the  substance 
exposes  to  attack,  and  for  a  given  weight  of  material  this 
increases  in  the  same  proportion  as  the  average  diameter 
of  the  particle  decreases.  In  consequence,  fineness  of 
grinding  is  perhaps  the  most  important  factor  in  deter- 
mining the  value  of  the  insoluble  phosphatic  manures, 
upon  it  more  than  even  upon  the  chemical  composition 
depends  the  availability  of  the  fertiliser  to  the  plant. 
Bone  meal  is  slow-acting  and  ineffective,  because  it  is 
coarse ;  nor  is  the  phosphoric  acid  brought  into  solution 
more  readily  in  the  second  year  than  in  the  first, 
because  the  coarse  condition  still  persists.  The  availa- 
bility of  a  phosphatic  fertiliser  might  even  be  reckoned 
as  the  product  of  two  factors :  a  solubility  factor  depending 
upon  its  chemical  composition,  and  a  second  factor — 
the  area  of  surface  of  unit  weight  of  the  material. 

If  bone  meal  has  been  overrated,  on  the  other  hand 
steamed  bone  flour  has  not  received  the  credit  it 
deserves.  In  the  first  place,  analysts  have  rather  warned 
the  farmer  against  steamed  bone  flour,  as  representing 
in  some  way  a  spurious  bone  meal  from  which  the 
nitrogen  had  been  illicitly  extracted.    The  warning  would 


v.]  BONE  FERTILISERS  155 

be  needful  enough  if  the  steamed  bone  flour  were  in  any 
way  being  passed  off  as  bone  meal,  but  provided  it  is 
sold  on  its  own  basis  as  a  material  containing  nearly 
sixty  per  cent,  of  tri-calcic  phosphate  and  one  per  cent, 
or  so  of  nitrogen,  it  is  a  better  manure  than  bone  meal. 
The  fine  grinding  of  the  steamed  bone  flour  allows  the 
phosphates  to  pass  into  solution,  while  the  extra 
nitrogen  of  the  raw  bone  is  so  slow  in  its  action,  that  as 
a  rule  it  would  pay  the  farmer  to  buy  steamed  bone 
flour  instead  of  bone  meal  and  to  make  up  this  deficiency 
by  the  addition  of  a  more  active  nitrogenous  material. 

Just  as  the  long-standing  knowledge  of  the  effect  of 
bones  has  given  rise  to  a  certain  prejudice  in  their 
favour,  which  is  reflected  in  the  fact  that  they  realise 
a  rather  higher  price  than  their  content  in  nitrogen  and 
phosphoric  acid  would  justify,  something  of  the  same 
tradition  exists  on  the  side  of  dissolved  bones  and  bone 
superphosphate.  There  is  no  experimental  evidence  to 
lead  one  to  expect  that  a  mixture  of  superphosphate 
and  sulphate  of  ammonia  will  not  give  as  good  results 
as  dissolved  bones  containing  the  same  amount  of 
nitrogen  and  phosphoric  acid  ;  indeed,  the  former  mixture 
will  probably  be  more  effective,  because  it  is  finer  and  in 
better  mechanical  condition.  And  yet  dissolved  bones 
is  generally  much  the  dearer  fertiliser :  for  example,  at 
the  time  of  writing,  the  price  of  dissolved  bones  in 
London  is  £^,  5s.  per  ton,  and  it  contains  275  per  cent, 
of  nitrogen  and  15  per  cent,  of  phosphoric  acid.  To 
supply  275  units  of  nitrogen,  2|  cwts.  of  sulphate  of 
ammonia  containing  20  per  cent,  of  nitrogen  will  be 
required,  and  this  costs  32s. ;  to  supply  15  units  of  phos- 
phoric acid  i\  tons  of  superphosphate  with  12  per  cent, 
of  phosphoric  acid  would  be  wanted,  and  this  would  cost 
£1,  2s.  6di.  For  32 +62-6  =  94s.  6d.,  therefore,  the  same 
amount   of    nitrogen    and    phosphoric   acid   could    be 


IS6  PHOSPHATIC  FERTILISERS  [chap. 

purchased  as  are  contained  in  the  ton  of  dissolved 
bones,  and  the  phosphoric  acid  would  be  wholly  soluble 
instead  of  partially,  as  in  the  bone  manure ;  there  is  a 
saving  of  los.  6d.  a  ton,  against  which  would  only 
have  to  be  offset  the  greater  carriage  on  the  extra 
8  cwts.  the  mixture  weighs. 

This,  of  course,  is  only  an  example  of  the  general 
fact  that  the  longer  a  fertiliser  has  been  known,  and  the 
greater  the  number  of  people  who  have  had  experience 
of  its  value  and  learnt  how  it  can  be  profitably  employed, 
the  better  will  be  its  standing  in  the  market,  and  the 
higher  its  price  per  unit  of  nitrogen,  phosphoric 
acid,  etc. 

It  has  already  been  stated  that  finely-ground  rock 
phosphates  are  occasionally  employed  as  fertilisers 
without  any  treatment  with  acid.  In  America  they 
are  often  obtainable  very  cheaply  in  comparison  with 
superphosphate  and  are  ground  to  an  extremely  fine 
powder,  so  that  on  the  basis  of  equal  money  value  they 
give  more  favourable  results  on  many  soils  than  the 
acid  phosphates.  In  Britain  they  have  proved  most 
effective  on  wet  and  peaty  soils ;  they  require  a  soil 
containing  plenty  of  organic  matter  to  generate  a 
comparatively  strong  solution  of  carbon  dioxide  in  the 
soil  water,  in  which  they  must  become  dissolved.  For 
the  same  reason  their  action  is  forwarded  by  the 
ploughing  in  of  green  crops  or  by  the  use  of  sulphate 
of  ammonia  as  a  source  of  nitrogen,  but  on  the  generality 
of  soils  they  form  but  ao  ineffective  source  of  phosphoric 
acid. 

It  will  thus  be  seen  that  it  is  impossible  to  arrange 
the  phosphatic  fertilisers  in  a  scale  of  value  depending 
upon  the  relative  availability  of  the  phosphoric  acid 
they  contain,  for  this  availability  is  mainly  determined 
by  the  soil,  and  will  vary  for  the  same  manure  from 


v.]  BONE  FERTILISERS  157 

soil  to  soil.  In  order  to  make  a  proper  choice,  the 
farmer  ought,  first  of  all,  to  know  how  much  carbonate 
of  lime  his  soil  contains,  and  in  the  light  of  his  know- 
ledge of  that  factor  and  of  the  general  character  and 
climate  of  the  soil,  he  will  decide  first  whether  he 
requires  a  basic,  acid,  or  a  neutral  phosphate,  and  then 
which  is  the  cheapest  inside  the  selected  class. 


CHAPTER  VI 

THE    POTASSIC    FERTILISERS 

Early  Use  of  Wood  Ashes — The  Stassfurt  Deposits — Manufacture 
and  Composition  of  commercial  Potash  Fertilisers  —  The 
Retention  of  Potash  by  the  Soil — The  Function  of  Potash  in 
the  Nutrition  of  the  Plant — Dependence  of  Carbohydrate 
Formation  upon  Potash,  as  illustrated  in  the  Barley  and  Man- 
gold Crops — The  Action  of  Nitrate  of  Soda  upon  insoluble 
Potash  Compounds  in  the  Soil — Potash  Fertilisers  as  promot- 
ing the  Growth  of  Leguminous  Plants— Efifects  of  Potash 
Starvation  upon  Vegetation — Potash  as  a  Preventive  of 
Fungoid  Disease — Potash  as  prolonging  the  Growth  of  the 
Plant— Destruction  of  the  Tilth  of  Clay  Soils  by  Potash  Salts 
— Soils  deficient  in  Potash. 

Although  the  water  cultures  already  described, 
coupled  with  the  results  of  the  Rothamsted  experiments 
even  in  their  early  years,  showed  that  of  the  alkali 
metals  found  in  the  plant's  ash  only  potassium  was 
indispensable,  for  a  long  time  the  salts  of  potash  could 
not  be  obtained  in  quantities  or  at  a  price  appropriate 
to  agricultural  requirements.  Almost  the  only  source 
of  potash  was  the  crude  carbonate  or  "  potashes,"  which 
was  obtained  by  dissolving  the  soluble  salts  found  in 
wood  ashes ;  and  though  this  was  to  a  small  extent 
supplemented  by  the  nitrate  of  potash  or  saltpetre 
obtained  from  India,  and  by  a  certain  amount  of 
sulphate  of  potash  obtained  from  "  kelp  " — the  ashes  of 
seaweed — no  widespread  use  could  be  made  of  potash 

158 


CHAP.  VI.]  tVOOD  ASHES  I59 

salts  in  farming  until  the  opening  up  of  the  great 
Stassfurt  deposits  in  Germany.  The  fertilising  value 
of  wood  ashes  had  long  been  known,  and'  in  the  south- 
east of  England  it  had  been  customary  for  the  hop- 
growers  to  organise  a  regular  system  of  collection  of 
the  ashes  of  their  cottagers,  who  burned  little  besides 
wood,  but  such  a  supply  was  only  local  and  early 
exhausted. 

William  Ellis,  again,  writing  in  1750,  states  that  "at 
Long  Marston,  in  Bucks,  is  a  potash  kiln,  where  they 
make  ashes  from  bean  straw  for  the  most  part,  and  sell  a 
vat  of  them,  which  contains  32  five-bushel  sacks,  which 
dresses  one  acre  for  fourteen  shillings,  to  be  shovelled 
out  of  a  cart  or  waggon,  and  throwed  over  grass  land  in 
this  month  (July)  or  at  any  time  till  Candlemass." 

In  1 86 1,  the  output  of  potash  salts  began  from 
Stassfurt  and  rapidly  grew,  until  in  1900  no  less  than 
1,158,000  tons  were  being  used  for  agricultural  purposes 
alone. 

The  German  potash  deposits  are  situated  near  the 
Harz  mountains,  and  centre  round  the  old  town  of 
Stassfurt,  where  for  a  very  long  time  common  salt 
had  been  manufactured  from  natural  brine  springs. 
A  boring  made  in  1858  proved  the  presence  of  rock- 
salt  at  a  little  more  than  1000  feet  below  the  surface, 
but  found  above  the  rock-salt  a  layer  of  minerals  con- 
taining potash  and  magnesia  salts,  which  were  at  first 
regarded  as  worthless  but  have  since  become  the  most 
valuable  substances  in  the  mine,  because  they  constitute 
the  only  known  source  of  potash  on  a  large  scale.  The 
deposits  occur  between  the  D3'as  and'  Trias  formations, 
and  are,  therefore,  of  much  the  same  age  as  the  salt- 
beds  of  Cheshire  and  Worcestershire,  and  like  them 
they  represent  the  result  of  the  drying  up  in  a  hot 
climate  of  a  great  lake  or  sea,  which  retained  some  con- 


i6o  THE  POT  AS  SIC  FERTILISERS  [chap. 

nection  with  the  ocean  so  as  to  admit  of  the  constant 
inflow  of  fresh  sea  water.  It  has  been  shown  that  all 
the  various  minerals — salts  of  sodium,  potassium, 
magnesium,  and  calcium — which  occur  in  these  deposits, 
are  formed  at  different  stages  in  the  concentration  and 
drying  up  of  a  solution  originally  of  the  composition  of 
sea  water,  and  the  sequence  of  their  deposition  has  led 
to  the  estimation  that  a  period  of  about  13,000  years 
was  necessary  for  the  formation  of  the  bed.  The 
sequence  of  deposits  varies  somewhat  from  shaft  to 
shaft,  especially  where  the  influx  of  water  in  the  past 
has  effected  some  rearrangement  in  the  salts ;  but  in 
the  main,  after  passing  through  600  to  800  feet  of  red 
sandstone,  limestone,  etc.,  a  bed  of  gypsum  is  first 
reached,  underneath  which  is  a  bed  of  very  pure, 
"younger"  rock-salt,  which  in  its  turn  gives  place  to  a 
bed  of  anhydrite  (anhydrous  sulphate  of  lime)  with 
some  gypsum.  Below  the  anhydrite  comes  a  bed  of 
tough  impervious  salt  clay,  which  has  acted  as  a  water- 
proof layer  and  prevented  the  solution  of  the  highly 
soluble  potash  and  magnesium  salts  immediately  below ; 
at  the  top  is  a  layer  50  to  130  feet  thick  of  carnallite, 
a  crude  double  chloride  of  potassium  and  magnesium 
which  is  the  main  source  of  the  manufactured  salts. 
Below  the  carnallite  comes  the  "  kieserite  "  region,  where 
this  mineral,  a  crude  sulphate  of  magnesia,  predominates, 
and  below  it  again  comes  a  "  polyhalite  "  region,  char- 
acterised by  the  prevalence  of  this  complex  sulphate  of 
potash,  lime,  and  magnesia.  The  polyhalite  overlies 
the  "  older "  rock  salt,  2000  feet  or  more  in  thickness, 
interspersed  with  and  underlaid  by  layers  of  anhydrite, 
before  the  limiting  bituminous  sandstones  are  reached. 
It  will  be  noticed  that  the  bottom  layer  of  anhydrite 
represents  the  least  soluble  salt  in  sea  water  ;  above  it 
comes  the  sodium  chloride  in  bulk ;  while  at  the  top  are 


VI.]  THE  STASSFURT  DEPOSITS  i6i 

gathered  together  the  magnesiurn  and  potassium  salts, 
which  would  be  the  last  to  remain  in  solution.  The 
manufacturing  is  extremely  simple  in  principle ;  the 
salts  of  the  potash  region,  chiefly  carnallite,  are  mixed 
and  brought  into  solution,  from  which  products  of 
various  grades  of  purity  can  be  obtained  by  evaporation. 
In  this  way  are  obtained  the  sulphates  and  muriates  of 
potash  of  commerce,  but  the  substances  chiefly  used  in 
agriculture  are  certain  crude  salts  contained  by  grinding 
suitable  mixtures  of  the  original  material  as  mined.  Of 
these  the  best  known  in  this  country  is  kainit,  a  mineral 
which,  properly  speaking,  only  occurs  in  some  of  the 
mines  where  water  had  formerly  access,  but  which 
commercially  represents  a  mixture  of  sulphates  and 
chlorides — chiefly  sulphates,  of  sodium,  potassium,  and 
magnesium,  containing  a  little  over  12  per  cent,  of 
potash. 

A  crude  "hard  salt"  or  "sylvinit,"  consisting  chiefly 
of  chlorides,  but  equally  containing  12  per  cent,  of 
potash,  is  put  upon  the  market  rather  more  cheaply 
than  the  kainit,  and  for  most  purposes  will  serve  equally 
well.  Owing  to  the  rapid  exhaustion  of  the  true  kainit 
deposits,  this  material  is  now  taking  the  place  of 
kainit  in  the  manure  market.  In  Germany  a  crude 
"carnallite"  of  still  lower  grade,  containing  only  about 
9  per  cent,  of  potash,  is  used,  but  its  hygroscopic  nature 
and  low  concentration  prevent  its  export  to  any  distance. 
Table  XL II.  shows  the  analyses  of  the  chief  Stassfurt 
products,  of  which  only  i,  3,  4,  and  6  come  to  this 
country  in  any  quantity. 

The  Stassfurt  salts  are  white  or  grey  or  pink  (owing 
to  the  presence  of  a  little  iron  as  impurity)  gritty 
powders,  which  dissolve  readily  and  almost  entirely,  and 
are,  as  a  rule,  more  or  less  deliquescent.  Potassium 
chloride,  and  particularly  magnesium  chloride,  are  very 

L 


l62 


THE  POT  AS  SIC  FERTILISERS 


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VI.]  OTHER  SOURCES  OF  POTASH  163 

soluble  and  greedy  of  moisture  ;  and  as  both  chlorides 
and  magnesium  are  present  in  all  but  the  purest  grades 
of  sulphate  of  potash,  the  salts  used  for  manurial 
purposes  are  always  somewhat  deliquescent. 

These  salts  constitute  practically  the  only  sources  of 
potash  for  manurial  purposes ;  wood  ashes  are  a  little 
used  occasionally,  a  small  amount  of  sulphate  of  potash 
is  derived  from  kelp,  and  the  ashes  which  form  the  final 
waste  product  in  beet  sugar  refining  are  used  for  the 
carbonate  of  potash  they  contain ;  but  the  whole  amount 
is  trifling  compared  with  the  increasing  output  of  the 
Stassfurt  mines. 

Attempts  have  been  made  from  time  to  time  to 
utilise  as  fertilisers  various  minerals  which  occur  in  large 
quantities  and  contain  considerable  amounts  of  potash ; 
for  example,  orthoclase  felspar,  KgAlgO^,  6Si02,  with  17 
per  cent,  of  potash,  and  leucite,  KgAlgO^,  2Si02,  with 
22  per  cent,  of  potash.  In  some  cases  these  minerals 
have  been  simply  reduced  to  a  very  fine  powder,  in 
others  they  have  been  heated  with  lime  or  soda  salts 
in  order  to  bring  the  potash  into  a  more  soluble  form. 
Though  the  results  show  that  the  potash  can  thus 
be  rendered  comparatively  available  for  the  plant, 
the  great  cheapness  of  the  completely  soluble  Stassfurt 
salts  has  prevented  any  general  adoption  of  the 
processes. 

The  question  of  which  of  these  salts  it  is  advisable 
to  apply  as  a  manure  has  excited  a  good  deal  of 
attention,  but  cannot  be  said  to  have  reached  any 
very  definite  settlement,  probably  because  the  problem 
is  complicated  by  a  secondary  action  of  the  salts  on  the 
texture  of  the  soil,  which  will  be  discussed  later.  But, 
speaking  generally,  it  may  be  said  that  for  grass  and 
mangolds,  and  wherever  the  salts  can  be  put  on  in  the 
winter  months  so  as  to  allow  the  magnesium  chloride 


I64  THE  POTASSIC  FERTILISERS  [chap. 

to  be  washed  away,  kainit  and  the  crude  salts  are  as 
effective,  potash  for  potash,  as  the  concentrated  salts  in^ 
which  the  unit  of  potash  is  more  expensive.  But  foj 
potatoes,  malting  barley,  and  similar  crops  where  qualit 
is  of  moment,  especially  when  the  manure  is  put 
near  the  time  of  seeding,  sulphate  of  potash  is  advisable, 
especially  upon  heavy  soils. 

Muriate  of  potash  has  often  been  shown  to  yield  a 
greater  weight  of  potatoes  than  sulphate,  though  the 
tubers  are  more  watery,  and  this  result  has  been 
associated  with  the  chlorine,  which  is  supposed  to 
assist  in  the  migration  of  starch  about  the  plant,  but 
the  facts  are  by  no  means  certain  as  yet. 

All  the  compounds  of  potash  found  in  these  fertilisers 
are  freely  soluble  in  water,  so  that  some  danger  of  loss 
by  washing  out  might  be  apprehended  when  the 
manures  are  applied  in  the  winter.  As  early,  however, 
as  1850,  Way  found  that  ordinary  soils  possessed  con- 
siderable powers  of  reacting  with  potash  salts  to  produce 
insoluble  potassium  compounds,  the  chlorine  or  sulphuric 
acid  of  the  salt  remaining  in  solution  combined  with 
calcium  and  other  bases  derived  from  the  soil.  The 
absorptive  power  was  found  to  be  greatest  with  soils 
rich  in  clay  and  humus,  and  the  retention  of  the 
potash  is  chiefly  effected  by  interaction  with  the  zeolitic 
double  silicates  of  the  clay,  potassium  being  exchanged 
for  calcium,  magnesium,  or  sodium  in  the  zeolite.  To 
a  certain  extent  a  similar  exchange  of  calcium  for 
potassium  takes  place  in  the  humus,  a  comparatively 
insoluble  potassium  humate  being  precipitated  and 
calcium  sulphate  or  chloride  going  into  solution. 

When  experiments  are  made  in  the  laboratory,  by 
treating  a  soil  with  a  weak  solution  of  potassium 
sulphate  or  chloride,  the  removal  of  the  potassium 
from   solution   is   never  complete ;   the  extent  of  the 


VI.]  RETENTION  OF  POTASH  BY  SOIL  165 

removal  will  in  any  case  depend  upon  the  relative 
masses  of  the  potassium  salt  and  the  zeolite,  so  that 
it  is  practically  complete  when  a  few  hundred  pounds 
of  fertiliser  are  applied  to  the  great  weight  of  soil 
which  represents  an  acre.  Voelcker's  analyses  of  the 
drainage  waters  collected  below  the  various  plots  at 
Rothamsted  showed  that  the  amount  of  potash  in  the 
water  flowing  from  the  drain  below  the  unmanured 
plot  was  1-7  parts  per  million,  and  was  only  increased 
to  2-9,  3-3,  4-4,  and  5-4  parts  respectively  on  other  plots 
which  are  annually  manured  with  300  lb.  per  acre  of 
potassium  sulphate.  Dyer's  examination,  also,  of  the 
soils  from  the  same  Broadbalk  wheat  field  show  that, 
of  the  potash  applied  as  manure  during  fifty  years  and 
not  removed  in  the  crops  grown  during  the  same 
period,  about  one-half  was  still  to  be  found  in  the  top 
9  inches  of  soil,  much  of  it  in  such  a  combination 
as  to  be  soluble  in  i  per  cent,  solution  of  citric  acid, 
while  further  quantities  of  the  applied  potash,  also 
soluble  in  the  weak  citric  acid,  were  to  be  found 
in  the  second  and  third  9-inch  layers  of  soil.  Thus, 
from  the  point  of  view  of  practice,  no  loss  of  potash 
need  be  apprehended  through  its  application  in  the 
winter  before  the  crop  is  occupying  the  land,  except 
on  the  lightest  sands  where  clay  and  humus  are 
lacking. 

To  understand  the  use  of  potassic  fertilisers  in  the 
ordinary  routine  of  farming,  it  is  necessary  to  enquire 
into  the  function  of  potassium  in  the  nutrition  of  the 
plant,  for  the  water  culture  experiments  hitherto 
quoted  only  demonstrate  that  it  is  one  of  the  indis- 
pensable elements. 

Further  enquiry  goes  to  show  that  in  some  way 
potash  is  an  essential  part  of  the  mechanism  of  the 
process  of  assimilation ;  when  it  is  deficient  the  manu- 


i66  THE  POTASSIC  FERTILISERS  [chap 

facture  of  carbohydrates,  like  starch,  sugar,  and  cellulose, 
is  greatly  reduced,  and  in  practice  it  is  the  crops  rich  in 
carbohydrate  which  are  most  dependent  upon  a  full 
supply  of  potash.  Reed  observed  that  starch  grains 
were  not  formed  in  the  cells  of  a  green  alga  immersed 
in  a  culture  fluid  containing  no  potash,  and  that 
those  originally  present  in  the  chlorophyll  gradually 
disintegrated  and  disappeared.  Some  earlier  experi- 
ments of  Hellriegel  and  Wilfarth  illustrate  the  depend- 
ence of  starch  formation  on  potash  even  more  clearly. 
They  started  a  series  of  water  cultures,  in  one  of  which 
the  supply  of  nitrogen  increased  in  successive  jars  from 
nothing  to  the  full  amount  required  for  the  plant ;  the 
other  constituents  were  fully  supplied  in  every  jar.  In 
a  second  series,  the  phosphoric  acid  supply  was  similarly 
varied,  and  in  a  third  series  the  potash.  As  would  be 
expected,  in  each  series  the  amount  of  dry  matter  grown 
was  roughly  proportional  to  the  supply  of  the  constituent 
which  was  in  defect.  Further,  when  nitrogen  or 
phosphoric  acid  was  lacking  the  formation  of  grain 
was  small,  but,  as  far  as  might  be,  the  grains  produced 
were  perfect ;  a  larger  number  of  grains,  but  not  bigger 
ones,  being  found  as  the  supply  of  nitrogen  or  phosphoric 
acid  increased.  Hence  the  weight  of  a  single  grain  was 
fairly  constant  whether  there  was  much  or  little  nitrogen 
and  phosphoric  acid.  But  when  potash  was  lacking  the 
individual  grains  were  small  and  undeveloped,  and  the 
average  weight  of  each  grain  increased  with  each 
addition  of  potash.  In  the  absence  of  potash  the 
assimilation  process  was  at  a  standstill,  hence  the 
grains  could  not  be  filled  with  the  starch  which  is 
their  main  constituent.  The  following  table  (XLIII.) 
shows  the  total  dry  matter,  the  percentage  of  grain, 
and  the  weight  of  a  single  grain  in  each  experiment 
of  the  three  series  : — 


VI.] 


GROWTH  OF  BARLEY 


167 


Table  XLIFI.— Growth  of  Barlev  with  increasing  Amounts  op 
Nitrogen,  Phosphoric  Acid,  and  Potash  (Hellriegel  and 
Wilfarth). 


NITROGEN  SERIES— OTHER  CONSTITUENTS  IN  EXCESS. 

Nitrogen 

Dry  Weight  of 

Com. 

Weight  of  One 

supplied. 

Produce. 

Grain. 

Mg. 

Grms. 

Per  cent. 

Mg. 

0 

0-7 

II-9 

19-5 

56 

4.9 

37-9 

27-0 

112 

IO-8 

38-0 

33-0 

168 

17-5 

42-6 

32-0 

280 

2I-2 

38-7 

31-5 

PHOSPHORIC  ACm  SERIES— OTHER  CONSTITUENTS  IN  EXCESS. 

Phosphoric  Acid 

Dry  Weight  of 

Corn. 

Weight  of  One 

supplied. 

Produce. 

Grain. 

Mg. 

Grms. 

Per  cent. 

Mg. 

0 

1-9 

... 

14.2 

8-3 

22-4 

27 

28-4 

12-6 

31-8 

29 

56-8 

19-5 

38-4 

38 

85-2 

19.5 

41-6 

34 

II3-6 

20-2 

43-8 

41 

142 

18.7 

41-3 

38 

213 

17-8 

40-1 

30 

2  84 

31-3 

43-4 

34 

POTASH  SERIES— OTHER  CONSTITUENTS  IN  EXCESS. 

Potash 

Dry  Weight  of 

Com. 

Weight  of  One 

supplied. 

Produce. 

Grain. 

Mg. 

Grms. 

Per  cent. 

Mg. 

0 

2-3 

23-5 

5-4 

4"8 

5-0 

47-0 

9-0 

21.5 

9-5 

70-5 

II-6 

27-2 

I3-0 

94 -o 

15-3 

30-I 

17.0 

I88-0 

21-2 

38-5 

260 

282-0 

29-8 

42-8 

34-0 

i68 


THE  POT  AS  SIC  FERTILISERS 


fCHAP. 


The  Rothamsted  results  with  barley  are  less  striking, 
because  of  the  large  amount  of  potash  originally  in  the 
soil;  it  is  only  during  the  later  years,  as  has  already 
been  explained,  that  any  deficiency  of  potash  has  been 
manifest  on  the  plots  that  do  not  receive  this  fertiliser. 
Still,  as  shown  in  the  following  table  (XLIV.),  which 
gives  average  results  for  the  fourteen  years  1 889-1902, 
the  use  of  potash  has  increased  both  the  weight  per 
bushel  and  the  weight  of  the  individual  grains  : — 


Table  XLIV.— Rothamsted  Barley  (14  years, 

1889-1902). 

Plot. 

Manuring. 

Weighti 
[per  Bushel. 

Weight 
of  100  Grains. 

lA 

2A 

3A 
4A 

Nitrogen  only 

Nitrogen  and  Phosphoric  Acid 
Nitrogen  and  Potash      . 
Nitrogen,    Phosphoric    Acid, 
and  Potash 

Lb. 

52-3 
52-2 

53-3 
53-8 

Grms. 

4-03 
3-86 
4.14 

4-21 

The  effect  of  potash  manuring  on  the  production  of  a 
carbohydrate,  in  this  case  sugar,  is  most  manifest  on  the 
mangold  crop.  If  Nos.  4  and  5  of  the  Rothamsted 
mangold  plots  which  receive  the  same  supply  of  nitrogen 
and  phosphoric  acid  are  compared,  it  will  be  found  that 
in  a  good  year  they  produce  approximately  the  same 
weight  of  leaf;  indeed,  the  similarity  would  be  still  closer 
if  the  comparison  were  made  when  the  leaves  were  in 
full  activity,  and  not  at  the  end  of  the  growing  season. 
One  plot  (4),  however,  receives  a  dressing  of  potash 
salts,  but  not  the  other  (5),  and  the  plot  with  potash 
produces  nearly  two  and  a  half  times  the  weight  ot 
roots  grown  upon  the  other  plot  without  potash.  Now 
the  difference  in  dry  weight  is  almost  wholly  due  to  sugar 
and  other  carbohydrates,  which  were  manufactured  in 
the  leaf  and  then  passed  on  to  the  root  for  storage ;  yet 


VI.] 


EFFECT  OF  POTASH  ON  MANGOLDS 


169 


the  two  plots  possessed  practically  the  same  leaf 
development,  working  under  identical  conditions  of 
illumination,  carbon  dioxide,  and  water  supply.  But 
in  one  case  the  photo-synthetical  process  had  been 
limited  by  the  want  of  potash ;  all  the  machinery  was 
there  and  the  power  was  in  excess,  but  the  machinery 
was  running  idle  for  the  lack  of  one  necessary  link — in 
this  case  the  potash  : — 

Table  XLV.— Effect  of  Potash  on  the  Produce  of  Mangolds 
at  rothamsted,  1900. 


Plot. 


Manure. 


Leaf 
per  acre. 


Roots 
per  acre. 


Sugar 
per  acre. 


5A 
4A 


Ammonium  Salts  and  Superphos- 
phate ..... 

Ammonium  Salts,  Superphosphate, 
and  Potash         .         .         •         . 


Tons. 
2'95 
3-25 


Tons. 
12  00 
28-95 


Tons. 
0-797 
2-223 


The  effect  of  potash  upon  the  mangold  crop  is  also 
to  be  seen  upon  the  plots  where  dung  is  also  supplied, 
as  shown  in  Table  XLVI. : — 

Table  XLVI.— Rothamsted  Mangolds  (12  years,  1895-1906). 


Manuring. 

No  Potash. 

+Phosphate3 
and  Potash. 

Dung  only  ...... 

„      and  Nitrate  of  Soda    .         . 

„      and  Ammonium  Salts 

„      and  Rape  Cake  .... 
Dung,  Rape  Cake,  and  Ammonium  Salts 

Tons. 
l8-6 

277 
21-8 
24.9 
24.2 

Tons. 

19-5 
26-8 
25-9 
28.6 
29.9 

Here  it  will  be  seen  that  potash  increased  the  crop 
in  every  case,  except  where  nitrate  of  soda  had  been 
used  as  the  nitrogenous  cross  dressing,  in  which  case 
the  soda   liberates  so    much  potash  from  the  soil  that 


I70  THE  POTASSIC  FERTILISERS  [chap. 

specific  application  of  potassic  manures  is  unnecessary. 
In  the  earlier  years  of  this  experiment  only  phosphates 
had  been  added  to  the  dung  and  nitrogenous  manures, 
but  had  produced  no  increase ;  we  may  conclude,  there- 
fore, that  in  the  series  quoted  it  was  the  potash  alone 
that  had  been  active.  This  result  is  the  more  striking, 
in  that  dung  itself  contains  a  large  proportion  of 
potash,  yet  the  use  of  14  tons  of  dung  per  acre  year 
after  year,  beginning  in  1856,  has  still  been  unable  to 
supply  the  mangold  crop  with  all  the  potash  it  needed. 

Both  in  this  series  of  plots  and  that  in  which  the 
mangolds  receive  no  dung,  the  value  of  potassic  manur- 
ings  is  small  where  nitrate  of  soda  is  the  source  of 
nitrogen.  This  is  not  only  because  the  sodium  can  be 
made  to  do  some  of  the  work  usually  done  by  potassium 
in  the  plant,  but  also  because  it  is  able  to  attack  the 
compounds  of  potash  in  the  soil  (the  Rothamsted  soil 
contains  an  enormous  reserve  of  insoluble  potash),  and 
bring  it  into  solution  so  that  it  becomes  available  for 
the  plant. 

This  can  be  illustrated  by  the  results  obtained  on 
the  Rothamsted  mangold  field  in  1900  (a  good  year); 
Table  XLVII.  shows  the  yield  of  roots  and  leaves,  and 
the  potash  and  soda  removed  from  the  soil  by  the  crop, 
both  with  and  without  potash,  when  the  nitrogenous 
manures  were  ammonium  salts  and  nitrate  of  soda 
respectively. 

It  will  be  seen  that  on  Plot  5N,  without  any  potash 
but  where  nitrate  of  soda  is  used,  the  yield  of  roots  and 
leaves  is  almost  as  great  as  that  obtained  on  6N  where 
potash  salts  are  also  added,  and  is  more  than  double  that 
given  by  the  corresponding  plot  without  potash,  5  A,  but 
which  receives  its  nitrogen  as  ammonium  salts.  The 
amount  of  potash  taken  from  the  soil  by  the  crop  on  Plot 
5N  is  927  lb.  against  596  lb.  on  5  A,  the  increase  repre- 


vi.l  SOIL  POTASH  RENDERED  SOLUBLE  BY  SODA  171 

senting  the  attack  of  the  soda  salt  upon  the  insoluble 
potash  in  the  soil,  but  it  will  be  seen  that  the  potash  thus 
present  in  the  crop  by  no  means  came  up  to  the  quantity 
removed  by  the  crops  on  6A  and  6N,  where  an  excess  of 
potash  had  been  applied  in  the  manure.  Since,  also,  the 
sum  of  the  two  alkalis,  potash  and  soda  together,  in 

Table  XLVII.— Potash  and  Soda  contained  in 
Mangolds.    Rothamsted,  1900. 


Plot. 

Roots. 

Leaves. 

Potash. 

Soda. 

Tons. 

Tons. 

Lb. 

Lb. 

5A 

Ammonium       Salts      and 

Superphosphate      . 

I2-00 

2-95 

59-6 

56-9 

6A 

Ammonium   Salts,   Super- 

phosphate, and  Potash  . 

28-20 

3 -60 

306-6 

67-0 

■^N 

Nitrate  of  Soda  and  Super- 

phosphate 

28-35 

3-85 

92.7 

251-6 

6N 

Nitrate    of    Soda,    Super- 

phosphate, and  Potash  . 

29-65 

3-60 

220-9 

1606 

the  crops  on  5N,  6 A,  and  6N  is  nearly  the  same,  it  may 
be  concluded  that  on  6A  and  6N  the  plant  was  taking 
up  a  much  greater  amount  of  potash  than  it  needed, 
due  to  the  excess  of  this  constituent  in  the  soil  and 
manure. 

Next  to  their  effect  upon  carbohydrate-making 
crops,  the  most  striking  action  of  potassic  manures  is 
their  value  in  promoting  the  growth  of  clover  and  all 
leguminous  crops.  The  function  of  potash  here  may  be 
still  that  of  prom^tinga^milatiDn,  because  the  bacteria 
which  fix  mtrogenin  the  nodules  on  the  roots  of  the 
leguminous  plants  must  be  supplied  with  carbohydrate 
by  the  plant  in  order  to  obtain,  by  its  oxidation,  the 
energy  requisite  for  the  fixation  of  nitrogen.  There  is 
evidence  to  show  that  the  fixation  of  nitrogen  by  these 
organisms  is  promoted  by  a  supply  of  carbohydrate ;  but 


/ 


172 


THE  POTASSIC  FERTILISERS 


[chap. 


whatever  may  be  the  explanation  it  is  found  in  practice 
that  the  growth  of  clover,  etc.,  is  very  much  promoted 
by  a  free  supply  of  potash,  and  this  is  very  manifest 
upon  sands  and  gravelly  soils  usually  poor  in  potash. 

This  effect  may  be  very  strikingly  seen  when  the 
fertiliser  is  applied  to  grass  land  carrying  a  mixed 
herbage,  for  the  potash  encourages  the  leguminous 
plants  until  the  aspect  of  the  vegetation  may  be 
entirely  changed.  On  the  Rothamsted  grass  land, 
which  is  mown  for  hay  every  year,  one  plot  gets  a 
complete  mineral  manure — phosphates  and  sulphates 
of  potash,  soda,  and  magnesia ;  the  adjoining  plot 
receives  the  same  phosphoric  acid,  magnesia,  and  soda, 
but  no  potash,  while  a  third  plot  gets  the  phosphates 
alone.  The  Table  XLVIII.  shows  the  comparative 
yield  and  the  composition  of  the  herbage  by  weight : — 

Table  XLVIII.— Rothamsted  Hay  Crop,  without  and  with 
Potash. 


Plot. 

Manuring. 

Dry  Hay. 

Composition  of  Herbage 
in  1902. 

1856 

to 

1902. 

1893 

to 

1902. 

Grasses. 

Legu- 
minous 
Plants. 

Weeds. 

7 
8 

4 

3 

Complete  Mineral 

Manure    . 

Do.        without 

Potash      . 
Superphosphate 

only 
Unmanured 

Cwts. 

38-8 

28.1 

23-3 
21.9 

'  Cwts. 

36.5 
21.6 

17-8 
iS-9 

Per  cent. 
20-3 

28-8 

54-4 
34-3 

Per  cent. 
55-3 

22  I 

15-4 
7-5 

Per  cent. 

24.4 

49-1 

30.2 
58-2 

On  the  plots  receiving  a  mineral  manure  including 
potash  half  the  vegetation  now  consists  of  leguminous 
plants,  but  in  the  absence  of  potash  the  proportion  is 


Vi.l      EFFECT  OF  POTASH  UPON  GRASS  LAND      173 

only  22  per  cent,  and  15  per  cent,  the  higher  proportion 
being  where  magnesia  and  soda,  which  attack  the  potash 
reserves  in  the  soil,  are  applied.  It  should  be  noticed 
that  the  large  amount  of  phosphoric  acid  received  by 
these  two  latter  plots  does  not  result  in  any  great 
stimulus  to  the  leguminous  plants,  which  constitute  7-5 
per  cent,  of  the  herbage  of  the  unmanured  plot.  Where 
nitrogen  is  applied  and  potash  omitted,  no  leguminous 
plants  are  to  be  found. 

On  these  grass  plots  another  very  striking  effect  of 
potash  manuring  is  also  very  manifest,  which  confirms, 
on  a  large  scale,  the  experiment  of  Hellriegel  and 
Wilfarth's  already  quoted.  On  the  potash-starved  plots 
the  grasses  fail  to  a  large  extent  to  develop  any  seed, 
and  the  heads  are  soft  and  barren,  presumably  because 
of  the  deficiency  in  carbohydrate  formation.  For  the 
same  cause  the  straw,  not  only  of  the  grasses,  but  also 
on  the  similarly  manured  wheat  and  barley  plots,  is 
always  weak  and  brittle  when  potash  is  wanting.  The 
plants  of  the  potash-starved  plots  at  Rothamsted  are 
also  characterised  by  certain  other  appearances,  which 
to  a  less  degree  are  to  be  observed  in  nature  where  the 
soil  is  naturally  poor  in  potash,  as  on  many  peaty  and 
sandy  lands.  The  grass  has  a  dull  colour,  partly  due 
to  a  deficiency  of  chlorophyll  and  its  substitution  by 
a  certain  amount  of  a  red  colouring  matter  along  the 
stems,  and  partly  because  the  tops  of  the  grass  blades 
show  a  great  tendency  to  die  off  for  an  inch  or  two  and 
leave  a  brown  withered  end.  When  in  1908  the  man- 
golds on  the  Barn  field  were  replaced  by  Swede  turnips, 
they  grew  with  considerable  vigour  and  remained  per- 
fectly healthy  on  the  potash-starved  plots,  except  that 
the  leaves  in  the  autumn  showed  a  flecked  appearance, 
especially  towards  the  margins,  where  a  good  deal  of 
the  leaf  tissue  had  a  yellow  brown  papery  look  which 


174  THE  POT  AS  SIC  FERTILISERS  [chap. 

marked   off  the  whole  plot   very  distinctly,  especially 
after  the  first  frosts  had  taken  place. 

There  is  abundant  experimental  evidence  to  show 
that  potash  makes  the  plant  more  resistant  to  the 
attacks  of  fungoid  diseases.  It  has  already  been 
explained  how  susceptible  the  use  of  nitrogenous 
manures  renders  the  mangolds  on  certain  of  the 
Rothamsted  plots  to  the  attack  of  a  leaf  spot  fungus 
— Uromyces  betae.  The  attack  is,  however,  much  less 
severe  on  the  plots  receiving  an  abundant  supply  of 
potash ;  there  the  plant  remains  healthy  even  though 
the  nitrogen  is  in  excess.  The  photograph,  Fig.  4, 
shows  two  typical  roots  taken  in  1902  from  plots  with 
and  without  potash,  both  receiving  the  same  large 
dressing  of  nitrogenous  manures. 

Just  in  the  same  way,  the  wheat  on  the  potash- 
starved  plots  is  always  subject  to  rust,  even  in  a  good 
season  when  very  little  is  to  be  seen  on  the  other  plots 
normally  manured.  The  grass  also  on  potash-starved 
plots  is  attacked  by  various  fungi ;  hence  it  may  be 
taken  as  a  general  rule,  that  crops  which  do  not  receive 
their  full  supply  of  potash  will  be  correspondingly  sus- 
ceptible to  disease. 

It  is  not  possible  to  say  whether  this  is  due  to 
any  specific  alteration  in  the  composition  of  the  cell 
contents  or  to  a  general  lack  of  vigour,  but  the  latter 
is  probable,  because  an  excess  of  potash  tends  to  pro- 
long the  vegetative  growth  of  the  plant  and  to  delay 
maturity.  Plants  receiving  potash  are  always  a  little 
the  greener,  especially  late  in  the  season,  and  this  is 
not  always  an  advantage,  as  may  be  seen  from  the 
fact  that  the  barleys  grown  on  the  plots  receiving 
potash  at  Rothamsted,  show  a  somewhat  darker  and 
less  attractive  colour  than  those  grown  without  potash. 
That  potash   tends   to   prolong   growth   may   also  be 


'O 


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cd  o 

VI.]  POTASH  MOST  EFFECTIVE  IN  DR  Y  SEASONS  175 

inferred  from  the  fact  that  its  effect  upon  the  yield  is 
always  most  pronounced  in  dry  seasons. 

Referring  again  to  Table  XXXIV.,  it  will  be  seen 
that  in  the  dry  season  of  1893,  the  yield  of  barley 
(grown  also  with  ammonium  salts  and  superphosphate) 
was  increased  by  a  dressing  of  potash  from  i8-i  to  30-8 
bushels  per  acre,  whereas  in  the  wet  season  of  1894  the 
increase  was  only  from  34-9  to  41-4  bushels  per  acre. 

Similarly  with  the  wheat  (Table  XXXV.,  p.  139), 
in  the  wet  season  the  application  of  potash  only 
increased  the  yield  of  grain  from  ii-i  to  i6-o  bushels, 
and  the  weight  from  54-6  to  57-8  lb.  per  bushel ;  whereas 
in  the  dry  season  the  yield  was  increased  from  77  to 
16-4  bushels  (more  than  double),  while  the  weight  was 
raised  from  56-4  to  62-6  lb.  per  bushel.  That  the  bad 
results  in  the  dry  year  were  due  to  a  premature  ripen- 
ing of  the  plant,  which  was  deferred  by  the  potash,  is 
seen  from  the  fact  that  with  potash  the  ratio  of  grain 
to  straw  was  98,  whereas  without  potash  it  only  reached 
67-3,  in  which  case  the  migration  of  materials  from  the 
straw  to  the  grain  is  clearly  incomplete.  But  though 
in  such  cases  of  grain  crops  the  use  of  potash  prolongs 
the  development  of  the  plant  and  defers  maturity, 
apparently  an  opposite  effect  is  produced  upon  root 
crops.  On  the  Rothamsted  field,  for  example,  where 
potash  is  used,  the  mangold  leaves  will  begin  to  turn 
yellow  and  fall,  indicating  that  the  plant  has  finished 
its  season's  growth,  long  before  any  such  appearance 
is  seen  on  the  potash-starved  plots  alongside,  where 
a  tuft  of  dark  green  and  apparently  growing  leaves 
persists  until  the  plant  is  cut  off  by  the  frosts.  Similar 
appearances,  though  in  a  less  pronounced  degree,  can 
be  seen  on  ordinary  crops  in  light  soils,  whenever  a 
strip  has  been  left  to  show  the  action  of  potash  in  the 
manure. 


176  THE  POT  AS  SIC  FERTILISERS  [chap. 

The  apparent  contradiction  may  be  explained  on 
physiological  grounds ;  with  the  root  crops  ripeness 
does  not  represent  the  completion  of  a  migration  process 
of  material  previously  stored  up,  such  as  takes  place 
from  straw  to  grain,  but  marks  the  completion  of  the 
work  of  the  leaves  in  manufacturing  carbohydrate  and 
passing  it  on  to  the  root  for  storage.  It  has  already 
been  shown  (Table  XLV.)  that  in  the  absence  of 
potash  the  leaves  cannot  carry  on  the  assimilation 
process  properly,  and  probably  they  continue  green 
instead  of  ripening  off  because  their  function  of  storing 
up  material  in  the  root  has  not  been  completed. 

From  time  to  time  field  experiments  have  been 
reported  which  show  a  reduced  yield  for  the  use  of 
potassic  salts,  and  while  in  many  cases  the  results 
might  be  put  down  to  experimental  error,  the  cases 
are  too  numerous  to  be  entirely  covered  by  such  an 
explanation. 

A  clue  to  this  apparent  depressing  effect  of  potash 
is  provided  by  the  appearance  of  the  soil  on  certain 
of  the  experimental  plots  at  Rothamsted,  as  on  the 
Barn  field,  where  considerable  amounts  of  potash  salts 
are  applied  every  year.  The  behaviour  of  the  soil, 
which  lies  extremely  wet  and  sticky  after  rain,  and  dries 
with  a  hard  glazed  surface,  shows  that  the  clay  particles 
must  have  become  thoroughly  deflocculated,  just  as  they 
are  on  the  plots  receiving  nitrate  of  soda  (p.  55). 

This  deflocculating  effect  of  the  potash  salts,  which 
in  themselves  would  flocculate  clay  particles,  is  due  to 
a  prior  interaction  between  the  potassium  salt  and  the 
calcium  carbonate  in  the  soil,  resulting  in  the  formation 
of  a  certain  amount  of  potassium  carbonate,  the  defloc- 
culating powers  of  which  have  already  been  recognised. 

The  destruction  of  tilth  of  the  soil  brought  about  in 
this  way  may  easily  give  rise  to  an  irregular  stand  and  so 


VI.]         SOILS  REQUIRING  POTASH  MANURES         177 

account  for  an  inferior  plant  and  a  reduced  yield  on  the 
plots  receiving  potash  salts ;  the  author  has  observed 
a  case  on  heavy  land  where  the  application  of  a  rather 
excessive  amount  of  kainit  so  altered  the  texture  of  the 
soil,  that  the  draught  of  ploughs  upon  it  was  perceptibly 
increased,  and  the  crop  suffered  to  a  marked  degree. 

The  examples  that  have  been  given  to  illustrate 
the  specific  action  of  potash  must,  however,  be  used 
with  some  caution  as  a  guide  to  the  manuring  of 
crops  under  ordinary  conditions  of  farming.  They  are 
extreme  cases,  drawn  mostly  from  the  later  years  of 
the  Rothamsted  experiments,  when  the  exhaustion  of 
the  available  potash  in  the  soil  had  become  very  pro- 
nounced through  the  continuous  cropping  with  the  help 
of  a  manure  containing  all  the  other  elements  of 
fertility  except  potash.  Except  on  special  soils  and 
with  the  specially  potash-loving  crops,  it  is  not  usual 
to  find  in  this  country  that  the  use  of  a  dressing  of 
potash  salts  has  any  visible  effect  on  the  yield,  so  large 
is  the  stock  of  potash  in  the  soil,  and  so  well  is  it 
conserved  by  the  ordinary  systems  of  cropping. 

On  the  lighter  soils,  the  sands  and  the  gravels, 
potash  is  most  likely  to  be  deficient,  and  the  ill-effects 
arising  from  its  absence  are  intensified  by  the  dryness 
of  these  soils.  Even  on  such  soils,  potash  manures  will 
rarely  be  found  remunerative  for  cereal  crops ;  for 
mangolds  and  potatoes,  and  to  a  less  extent  for  turnips, 
they  are  necessary ;  while  grass  land  can  hardly  be 
maintained  in  a  satisfactory  character  without  potash 
at  regular  intervals.  On  the  stronger  soils,  potash  is 
a  remunerative  manure  for  mangolds,  and  occasionally 
for  land  laid  up  for  hay ;  but  in  general,  the  use  of 
nitrate  of  soda  as  a  source  of  nitrogen  will  liberate 
enough  of  the  locked-up  potash  in  the  soil  for  the  needs 
of  the  crop. 

M 


CHAPTER  VII 

FARMYARD    MANURE 

Variable  Composition  of  Farmyard  Manure — The  Fate  of  the 
Constituents  of  Food  during  Digestion  and  Excretion — 
Composition  of  Urine  and  Fasces  of  Farm  Animals  — 
Fermentation  Changes  taking  place  during  the  Making  of 
Dung — The  Breakdown  of  the  Nitrogenous  Bodies  and  of 
the  Carbohydrates — Gases  found  in  the  Dunghill — Losses  of 
Nitrogen  during  the  making  of  Farmyard  Manure — Pre- 
servatives used  to  minimise  the  Losses  during  Dung-making — 
Composition  of  Farmyard  Manure — Cake-fed  v.  Ordinary 
Manure — Long  and  Short  Manure — London  Dung — The 
Value  of  Fresh  Manure — The  Fertilising  Value  of  Farmyard 
Manure — Recovery  of  its  Nitrogen  in  the  Crop  —  Long 
Duration  of  the  Action  of  Farmyard  Manure — Farmyard 
Manure  as  a  Carrier  of  Weeds  or  Disease — The  Physical 
Effects  of  Farmyard  Manure  upon  the  Soil — The  Improvement 
in  Texture  and  Water-retaining  Power — Value  of  Farmyard 
Manure  as  a  Mulch  on  Grass  Land — Farmyard  Manure  best 
utilised  for  the  Root  Crop  or  Grass  Land — Value  of  Farmyard 
Manure  :  Cost  of  making  One  Ton. 

Farmyard  manure,  foldyard  manure,  yard  manure,  and 
dung  are  all  terms  employed  in  various  parts  ol  the 
country  for  the  same  more  or  less  decomposed  mixture 
of  the  excreta  of  domestic  animals  with  the  straw  or 
other  litter  that  is  used  in  the  yards  or  stalls  to  absorb 
the  liquid  portions  and  keep  the  animal  clean.  Probably 
it  would  be  more  correct  to  retain  dung  as  a  name  for 
the  excreta  alone,  and  farmyard  manure  for  the  product 
that  leaves  the  yards,  but  it  is  impossible  in  practice  to 
observe  any  such  distinction.     It  follows,  from  its  origin, 

178 


CHAP.  vii.J  PROCESS  OF  DIGESTION  179 

that  the  composition  of  farmyard  manure  must  be  far 
from  constant,  varying  with  the  nature  of  the  animal 
making  the  dung,  the  kind  and  amount  of  food  it 
receives,  the  proportion  between  excreta  and  litter, 
the  nature  of  the  litter,  and  the  extent  and  character  of 
the  decomposition  which  has  taken  place  in  the  manure 
itself.  The  composition  of  the  excreta  being  the  largest 
of  these  factors,  it  will  be  necessary  first  of  all  to  trace 
the  effect  of  the  process  of  digestion  on  the  various 
manurial  substances  in  the  food — compounds  of  nitrogen, 
phosphoric  acid,  and  potash.  Animals  that  are  not 
increasing  in  weight,  such  as  working  horses  or  full- 
grown  cattle  simply  being  maintained  in  store  condition, 
excrete  the  whole  of  the  nitrogen,  phosphoric  acid, 
and  potash  they  receive  in  a  liquid  or  solid  form, 
the  carbohydrates  and  fat  of  the  food  being  mostly 
got  rid  of  as  gases.  But  the  fate  of  the  manurial 
constituents  varies  according  as  they  are  present  in  the 
food  as  digestible  or  indigestible  compounds ;  for 
example,  part  of  the  proteins  of  the  food  withstand 
the  action  of  the  digestive  ferments,  and  are  excreted 
unchanged  in  the  fceces,  but  to  a  much  greater  extent 
they  are  broken  down  into  soluble  compounds  which 
pass  into  the  blood  and  eventually  are  excreted  as 
urea,  uric  acid,  etc.,  in  the  urine.  Similarly,  for  the 
phosphoric  acid  and  the  potash  in  the  food,  whatever 
is  digestible  is  excreted  in  the  urine  in  some  simpler 
combination,  whatever  resists  digestion  passes  out 
unchanged  in  the  solid  excreta.  Hence  a  great 
difference  in  the  manurial  value  of  the  two  portions  of 
the  excreta ;  the  compounds  in  the  urine — urea,  uric 
acid,  soluble  phosphates,  and  potash  salts — are  either 
ready  for  the  nutrition  of  plants  or  require  but  slight 
further  changes  to  become  so  ;  whereas  in  the  solid 
dung  the  materials  have  several  stages  of  decomposition 


i8o 


FARMYARD  MANURE 


[chap 


to  go  through  before  they  can  reach  the  plant,  and 
having  already  shown  themselves  able  to  resist  the 
attack  of  the  animal's  digestive  ferments  they  are 
correspondingly  unaffected  by  the  ordinary  decay 
processes  in  the  soil.  The  proportion  the  digestible 
bear  to  the  indigestible  constituents  of  a  food  varies 
with  the  nature  and  even  with  the  mechanical  condition 
of  the  material,  also  with  the  kind  and  age  of  the 
animal ;  roughly  speaking,  the  richer  the  food  the 
greater  the  proportion  that  is  digestible — ^.^..decorticated 
cotton  cake  contains  7  per  cent,  of  nitrogen,  of  which 
87  per  cent,  is  digestible  and  finds  its  way  into  the 
urine,  while  hay  contains  about  1-5  per  cent,  of  nitrogen, 
of  which  only  50  to  60  per  cent,  is  digestible. 

When  the  animal  consuming  the  food  is  growing  or 
fattening  or  yielding  milk,  a  certain  proportion  of  the 
manurial  constituents  in  the  food  is  retained,  the 
proportion  varying  with  the  nature  both  of  the  food 
and  the  animal.  Cows  in  milk  and  young  growing 
animals  take  the  greatest  toll  from  their  foods,  animals 
in  the  later  stages  of  fattening  the  least.  If,  for 
example,  100  lb.  of  linseed  cake  be  fed  to  milch  cows 
and  oxen  nearly  fat  respectively,  the  manurial  con- 
stituents contained  in  the  cake  will  be  distributed  in 
each  case  as  shown  in  Table  XLIX. 


Table  XLIX. — Nitrogen  Retained  and  Digested. 


In 
100  lb. 
Cake. 

Fattening  Oxen. 

Milch  Cowa. 

In 
Meat. 

In 
Urine. 

lu 

Psece*. 

In 

Milk. 

In 
Urine. 

In 
Faeces. 

Nitrogen 

Phosphoric  Acid   . 
Potash  . 

4-75 

2-0 

1-4 

0-2I 
0-14 
0-02 

3-88 
0-09 

I-IO 

0-66 
1-77 

0-28 

I-?2        2-75 
0-5        0-07 
0-14       1-05 

0.66 
1-43 
0-21 

VII.] 


COMPOSITION  OF  EXCRETA 


i8i 


It  is  thus  impossible  to  state  the  composition  of  the 
excreta  of  the  various  farm  animals  except  within 
certain  wide  limits,  owing  to  the  variations  induced  by 
the  food  and  the  age  of  the  animal.  Table  L.  shows 
certain  average  results  which  will  serve  to  characterise 
the  different  animals. 


Table  L.— Composition  of 

Urine  and  Excreta. 

Animal. 

Excreta. 

Water. 

Nitrogen. 

Phosphoric 
Acid. 

Potash. 

Horse    .         •  < 
Cow     .        .     1 
Sheep  .        .     \ 
Pigs      .        .  { 

solid 
liquid 

solid 
liquid 

solid 
liquid 

solid 
liquid 

75-0 
90 -o 

86-0 
91.5 

57-6 
86.5 

76-0 
97.6 

0-56 
1-52 

0-44 
1-05 

0-72 
I-3I 

048 
0-50 

0-35 
trace 

0-12 

trace 
0-44 

O-OI 

0-58 
0-14 

O-I 

0-92 

0-04 
1-36 

0-36 
0-70 

It  will  be  seen  that  the  urine  of  sheep  and  horses  is 
much  more  concentrated  than  that  of  cattle  and  pigs ; 
similarly,  the  solid  excreta  of  the  two  former  are  also 
the  drier.  It  is  this  greater  dryness  and  richness 
which  causes  the  gardener  to  describe  horse  manure  as 
"hotter"  than  that  produced  by  either  cows  or  pigs; 
bacterial  changes  take  place  in  it  much  more  rapidly,  a 
greater  amount  of  ammonia  is  produced,  and  the  rise 
of  temperature  is  more  pronounced. 

The  next  factor  which  enters  into  the  composition 
of  the  dung  is  the  nature  of  the  litter  on  which  the 
animals  are  placed ;  from  time  to  time,  especially  among 
small  holders,  various  materials,  such  as  bracken  fern, 
hop  bine,  leaves,  even  manufacturing  refuse  like  spent  tan 
and  sawdust,  are  used  ;  but  on  a  large  scale  only  two — 
straw  and  to  a  less  extent  peat  moss  litter,  get  employed. 


l82 


FARMYARD  MANURE 


[chap. 


The  litter  has  a  twofold  function :  it  absorbs  the  urine 
and  other  liquid  portions,  and  it  provides  both  organic 
matter  and  nitrogen  for  the  resulting  manure.  The 
cereal  straws  contain  about  0-5  per  cent,  of  nitrogen, 
0-2  per  cent,  of  phosphoric  acid,  and  i-o  per  cent,  of 
potash,  the  variations  in  composition  between  individual 
samples  of  any  one  kind  of  straw  being  as  great  as 
the  variation  between  average  samples  of  wheat,  oat, 
and  barley  straw.     Speaking  generally,  straw  grown  in 


Table  LL— Composition  of 

Litter. 

Water. 

Organic 

Matter. 

Ash. 

Nitrogen. 

P205. 

K^O. 

I.  Wheat   Straw  (W^et 

Season) 

17-8 

76-2 

6-0 

0-38 

0-19 

0-77 

2.  Wheat  Straw   (Dry 

Season) 

15-6 

78.9 

5-5 

0-2 1 

0.17 

I-OO 

3.  Oat  Straw 

16.5 

77-9 

5-6 

0-4 

0-28 

0-97 

4.  Barley  Straw  . 

20-0 

74.6 

5-4 

0.27 

o-i8 

0-45 

5.  Bracken  .        , 

13-6 

81.7 

4-7 

1.44 

0-20 

O-II 

6.  Hop  Bine        , 

18.7 

77-3 

3-95 

0.28 

0-07 

O-IO 

7.  Peat  Moss       , 

31-8 

47-6 

20-6 

0.83 

O-IO 

0.17 

the  north  of  England  and  Scotland  is  richer  than  straw 
grown  in  the  south  and  east  of  England,  because  the 
vegetative  growth  has  been  more  prolonged  and  the 
migration  of  food  materials  from  the  straw  into  the 
corn  has  not  been  quite  so  thorough.  Straw  will  absorb 
from  two  to  three  times  its  weight  of  water,  and  again 
the  variation  in  absorbing  power  between  different 
samples  of  the  same  kind  of  straw  is  greater  than  that 
between  different  kinds  of  straw.  In  practice  wheat 
straw  is  the  most  highly  esteemed,  as  cleaner  and 
wearing  better  under  the  feet  of  the  animals  than  any 
other  kind  of  straw.  Oat  straw  comes  next,  and  is  often 
almost  as  good  as  wheat  straw ;  barley  straw  is  least 
liked,  as  it  is  often  brittle  and  dusty. 


VII.] 


FUNCTION  OF  LITTER 


1S3 


Peat  moss  litter  consists  of  humified  vegetable 
matter,  being  derived  from  the  upper  layers  of  a  peat 
bog,  where  the  material  still  retains  a  good  deal  of  its 
original  structure ;  it  forms  a  brown,  spongy,  fibrous 
mass  consisting  almost  wholly  of  organic  matter.  It 
will  absorb  a  greater  amount  of  water  than  will  an 
equal  amount  of  straw,  up  to  about  ten  times  its  own 
weight  of  water.  Peat  moss  is  also  remarkable  for  its 
power  of  absorbing  ammonia  even  from  the  atmosphere, 
so  that  a  stable  littered  with  peat  moss  will  remain 
sweet  for  a  comparatively  long  time.  Table  LI  I.  shows 
the  result  of  an  experiment  in  which  two  similar 
stables  carrying  the  same  stock  were  littered — the  one 

Table  LII. — Ammonia  in  Stable  per  Million  of  Air. 


Litter. 

1st 
day. 

2nd 
day. 

3rd 
day. 

4th 
day. 

5th 
day. 

6th 
day. 

inh 

day. 

Straw  .     . 
Peat  Moss 

•0012 
0 

•0028 
0 

•0045 
0 

•0081 
0 

•0153 
trace 

•0168 
•001 

•017 

with  straw,  the  other  with  peat  moss,  and  the  amount 
of  ammonia  in  the  air  was  determined  every  day. 
As  will  be  seen,  the  peat  moss  proved  a  much 
more  efficient  absorber  of  the  ammonia  produced  than 
the  straw.  The  peat  moss  itself  usually  contains  a 
higher  proportion  of  nitrogen  than  straw  does,  hence 
the  manure  it  makes  appears  to  be  correspondingly 
richer,  and  this  difference  is  often  increased  by  its 
longer  retention  in  the  stalls.  But  the  peat  moss 
itself  is  very  slow  to  decay,  especially  in  dry  soils, 
so  that  it  is  doubtful  whether  its  extra  content  in 
nitrogen  is  of  much  value  ;  direct  experiments,  however, 
are  lacking  to  compare  the  relative  value  of  manure 
made  from  the  same  amount  of  feeding  stuffs  with  peat 
moss  and    straw  respectively.      Peat    moss  manure  is 


i84  FARMYARD  MANURE  [chap. 

always  short,  and  is  less  easy  to  handle  in  consequence, 
but  it  requires  no  making  and  can  be  applied  straight 
from  the  yards  even  to  the  lightest  of  soils. 

However  the  farmyard  manure  has  been  made,  it 
thus  starts  with  a  mixture  of  excrement,  urine,  and 
litter,  which  become  more  or  less  consolidated  and 
mixed  together  by  the  trampling  of  the  animals.  Other 
changes,  however,  intervene  very  rapidly,  and  these  in 
the  main  are  brought  about  by  bacteria,  which  for 
convenience  may  be  divided  into  two  groups,  one  acting 
on  the  cellulose  and  other  carbon  compounds  of  the 
straw  that  make  up  the  bulk  of  the  manure,  and  the 
other  acting  on  the  nitrogenous  compounds  that  do  not 
weigh  so  much  but  supply  the  main  fertilising  properties 
of  the  dung. 

Among  the  more  important  of  the  organisms  dealing 
with  nitrogenous  material  are  those  which  attack  the 
urea  in  the  urine  and  by  adding  to  it  the  elements  of 
water  give  rise  to  a  carbonate  of  ammonia,  which  very 
readily  dissociates  into  free  ammonia  and  carbonic  acid 
— both  gases,  and  therefore  capable  of  escaping  into 
the  atmosphere. 

CO(NH2)2  +  2H20  =  (NHJ2CO3  =  2NH3  +  CO2  +  H2O 

There  exists  more  than  one  organism  bringing 
about  this  change,  but  the  best  known  is  a  small  coccus 
known  as  Micrococcus  urecB,  which  is  widely  disseminated 
in  the  air  and  dust,  and  is  naturally  extremely  abundant 
in  such  places  as  stables  and  cattle  stalls,  where  it  is 
always  giving  rise  to  ammonia.  This  change  into 
ammonium  carbonate  is  an  extremely  rapid  one;  in 
the  liquid  draining  from  a  yard  or  a  manure  heap,  or 
even  in  the  liquid  manure  tank,  little  or  no  urea  can  be 
detected,  so  complete  has  been  the  change  to  ammonia. 
As  long  as  the  liquid  containing  the  ammonium  car- 


VII.]  CHANGES  IN  THE  COMPOSITION  OF  DUNG   185 

bonate  is  protected  from  evaporation,  no  loss  of  nitrogen 
will  result,  but  the  more  surface  it  exposes  to  the  air 
and  the  higher  the  temperature,  the  greater  will  be  the 
amount  of  ammonia  passing  off  in  a  gaseous  condition. 
Thus  thin  films  of  urine  on  the  floors,  walls,  or  even  on 
the  surface  of  loose  straw,  easily  lose  nitrogen  by  the 
fermentation  of  the  urea  and  subsequent  volatilisation 
of  the  ammonia;  the  smell  of  a  stable  arises  in  this  way 
and  is  clear  evidence  of  the  escape  of  ammonia.  As 
will  be  brought  out  more  clearly  later,  this  volatilisation 
of  ammonia  causes  most  of  the  loss  of  nitrogen  that 
takes  place  in  making  dung. 

The  ammonium  carbonate  is  itself  subject  to  change 
and  even  to  loss  by  other  actions  than  evaporation : 
there  are  always  present  in  the  manure  heap  various 
bacteria  which  can  oxidise  ammonia  into  free  nitrogen 
gas  and  water ;  in  consequence  dung  which  is  allowed 
to  lie  about  loosely  grows  poorer  in  nitrogen  from  this 
cause  as  well  as  through  volatilisation  of  ammonia. 
Though  the  action  has  been  recognised  as  taking  place 
in  practice,  little  is  known  of  the  specific  bacteria  which 
set  free  gaseous  nitrogen  in  this  way,  a  process  which 
is  often  called  "  denitrification,"  though  the  term  is 
better  restricted  to  the  change  whereby  nitrates  are 
reduced  to  nitrogen  gas.  Nor  have  the  conditions 
favourable  to  this  change  been  closely  investigated ;  it 
is,  however,  certain  that  rapid  oxidation  such  as  is 
brought  about  by  a  loose  condition  of  the  manure  or  by 
turning  it,  will  be  accompanied  by  some  destruction  of 
ammonia.  It  is  also  favoured  by  the  presence  of  soluble 
carbohydrates — i.e.^  easily  oxidisable  material — and  it  is 
materially  reduced,  if  not  suspended,  as  soon  as  these 
substances  have  been  used  up. 

Another  group  of  bacteria  which  are  extremely 
abundant  in  fresh  faeces  are  the  so-called  putrefactive 


r86  FARMYARD  MANURE  [chap. 

bacteria  which  break  down  the  proteins  into  simpler 
compounds  such  as  amino-acids,  amides,  and  finally 
ammonia.  Some  of  these  bacteria,  like  B.  coli  communis, 
are  abundant  in  the  large  intestine  of  herbivorous 
animals,  and  of  course  continue  their  work  in  the  excreta 
after  ejection.  Without  discussing  them  individually, 
their  function  is  to  convert  the  insoluble  nitrogenous 
bodies  of  the  straw  (those  of  the  faeces  are  more  difficult 
of  attack  because  they  have  already  resisted  the  actions 
of  digestion)  into  soluble  bodies  akin  to  ammonia  and 
therefore  more  nearly  utilisable  by  the  plant.  Thus, 
with  a  certain  amount  of  loss  as  free  nitrogen,  the  trend 
of  the  bacterial  actions  taking  place  in  the  fresh  farm- 
yard manure  is  to  break  down  the  complex  insoluble 
compounds  of  nitrogen  to  more  and  more  simple  ones, 
ammonia  being  the  final  term.  At  the  same  time,  there 
is  always  a  reverse  change  going  on  ;  as  the  bacteria 
themselves  multiply,  they  seize  upon  the  active  soluble 
forms  of  nitrogen  and  convert  them  into  insoluble 
proteins  in  their  body  tissues.  Which  action  is  pre- 
dominant will  depend  on  the  stage  that  has  been 
reached  in  the  dung-making  process — i.e.^  on  the  supply 
of  carbohydrate,  air,  water,  and  other  variable  factors — 
but  after  the  first  rapid  production  of  ammonium  com- 
pounds, the  longer  the  dung  is  stored  the  more  the 
ammonia  returns  to  a  protein  form. 

So  far  we  have  been  considering  only  changes  in 
the  nitrogenous  material  of  the  excreta  and  the  litter, 
since  nitrogen  is  the  chief  fertilising  constituent  of  the 
manure,  but  the  most  characteristic  change  in  dung- 
making  is  the  destruction  of  the  straw  and  its  con- 
version into  dark  brown  "humus,"  which  in  the  end 
retains  none  of  the  structure  of  the  original  straw. 
There  are  a  number  of  organisms  to  be  found  commonly 
in  the  air  and  dust  which  readily  attack  such  carbo- 


VII.]  CHEMICAL  CHANGES  DURING  DUNG-MAKING  187 

hydrate  material  as  straw  affords,  and  in  the  presence 
of  oxygen  burn  it  up  completely  into  carbon  dioxide, 
water,  and  inorganic  ash.  Such  organisms,  however, 
do  not  play  a  very  large  part  in  manure-making, 
because  oxygen  soon  gets  excluded  from  the  mass ; 
the  work  is  taken  up  instead  by  other  bacteria 
capable  of  working  in  the  absence  of  oxygen.  Two 
of  these  only  have  been  as  yet  studied  in  any 
detail ;  they  both  rapidly  attack  carbohydrates  like 
cellulose,  and  give  rise  to  carbon  dioxide,  marsh 
gas  or  hydrogen  respectively,  certain  fatty  acids,  of 
which  butyric  is  the  chief,  and  the  indefinite  brown 
acid  substance  known  as  "humus,"  which  is  richer  in 
carbon  than  the  original  carbohydrate.  The  evolution 
of  such  gases  can  easily  be  demonstrated  during  the 
making  of  dung,  either  by  laboratory  experiments  or 
by  an  analysis  of  the  gases  extracted  from  a  dunghill. 

Table  LI  1 1,  shows  the  gases  extracted  from  a  fresh 
dunghill  by  Deherain  during  one  of  his  experiments  at 
Grignon. 

When  the  first  sample  was  taken,  the  dungheap  was 
still  in  process  of  formation,  and  was  in  too  dry  a 
condition.  The  hydrogen  fermentation  was  most 
prominent  at  this  stage,  and  hydrogen  and  carbon 
dioxide  were  the  most  prominent  gases.  On  that 
day  the  liquid  manure  was  pumped  up  over  the 
whole  mass,  and  fermentation  became  more  active,  as 
seen  by  the  very  high  temperatures  reached  on  the 
24th,  when  the  formation  of  hydrogen  had  diminished, 
while  that  of  marsh  gas  had  increased  greatly.  The 
analyses  on  30th  August  show  the  result  of  having 
again  let  the  heap  get  dry ;  the  top  and  middle  were 
full  of  air,  as  may  be  seen  from  the  large  proportions 
of  nitrogen  and  the  presence  of  some  oxygen;  the 
percentage    of   carbon   dioxide    had    also   become   so 


1 88 


FARMYARD  MANURE 


[chap. 


low  that  losses  of  ammonia  would  take  place  by 
volatilisation,  especially  as  the  temperature  was  high. 
The  later  analyses,  taken  when  the  heap  was  well 
consolidated    and    kept    moist,    show    that    a    steady 

Table  LI  1 1. —Composition  of  Gases  in  Dunghill  (Deherain). 


Date, 

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Oct.  4    . 

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J.    middle 

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517 

0-0 

anaerobic  fermentation  of  carbohydrates  into  equal 
volumes  of  carbon  dioxide  and  marsh  gas  was  then 
going  on,  while  the  evolution  of  hydrogen  had  stopped. 
From  these  and  the  other  analyses  executed  by 
Deherain,  it  may  be  learnt  that  the  main  anaerobic 
fermentation  which  takes  place  when  the  straw  and 
other  materials  are  fresh,  is  that  which  gives  rise  to 
hydrogen  and  carbon  dioxide ;  if  the  heap  gets  too 
dry  and  air  penetrates,  an  aerobic  fermentation  begins, 
which  gives  rise  to  carbon  dioxide  only ;   but  at  the 


Vii.]CBEMICAL  CHANGES  DURING  DUNG-MAKING  189 

same  time  the  proportion  of  this  gas  falls  to  such  an 
extent  because  of  its  dilution  with  the  air,  that 
ammonia  can  be  lost  by  volatilisation.  By  consolidat- 
ing the  heap  and  pumping  the  liquid  over  it  afresh, 
the  anaerobic  fermentation  rapidly  sets  in  again  and 
the  proportion  of  carbon  dioxide  is  restored,  thus 
checking  the  dissociation  and  volatilisation  of  the 
ammonium  carbonate.  After  the  first  outburst  of 
fermentation,  the  evolution  of  hydrogen  ceases  and 
the  marsh-gas  fermentation  takes  its  place. 

A  considerable  proportion,  amounting  to  one-quarter 
or  more,  of  the  dry  matter  of  the  original  dung  is  lost 
during  this  process  of  humification,  by  the  conversion 
of  carbohydrates  into  carbon  dioxide,  marsh  gas  or 
hydrogen,  and  water.  The  various  acids  which  are 
also  produced  are  neutralised  by  the  liquid  part  of 
the  manure,  which  is  alkaline  from  the  presence  of 
ammonium  and  potassium  carbonates  resulting  from 
the  fermentation  of  the  nitrogenous  constituents  and 
salts  of  the  urine ;  the  dark  brown  liquid  to  be  seen 
draining  from  a  dunghill  is  a  solution  of  the  humus 
formed  in  this  alkaline  liquid. 

The  changes  going  on  during  the  making  and 
storage  of  farmyard  manure  are  thus  exceedingly 
complex ;  it  is  in  the  early  stages  that  the  bacterial 
actions  are  most  rapid,  and  they  fall  chiefly  upon 
the  soluble  nitrogenous  compounds  like  urea.  At  this 
time  the  greatest  losses  of  nitrogen  take  place  both  by 
volatilisation  of  ammonia  and  by  evolution  of  nitrogen 
gas,  and  so  active  is  the  oxidation  that  the  temperature 
of  the  mass  rises  continually.  If  the  rate  of  oxidation 
b2  promoted  by  occasionally  turning  over  the  mass,  as 
in  preparing  a  hot  bed  or  a  mushroom  heap,  the  rise 
in  temperature  is  much  increased  ;  at  the  same  time 
the  losses  of  nitrogen  rise  rapidly,  and  the  amides  and 


tgo  FARMYARD  MANURE  [chap. 

ammonium  carbonate  disappear  more  quickly.  What 
the  gardener  calls  "  taking  the  fire  "  out  of  the  manure, 
means  so  reducing  the  free  ammonia  that  the  material 
is  no  longer  injurious  to  a  plant's  roots,  though  it  still 
remains  rich  in  nitrogen  and  organic  matter  capable  of 
further  decay.  As  soon  as  the  first  violent  reactions  are 
over,  especially  after  the  mass  has  become  consolidated 
by  trampling  and  the  oxygen  in  the  entangled  air  has 
been  used  up,  the  rate  of  change  slows  down  consider- 
ably ;  it  now  consists  mainly  in  the  attack  of  the 
anaerobic  organisms  upon  the  carbohydrate  material. 
The  long  strawy  dung  begins  to  change  to  "  short "  or 
rotten  manure,  and  this  change  may  continue  slowly  for 
years,  until  all  trace  of  structure  is  entirely  gone  and 
only  a  brown  pulp  is  left.  During  this  second  change 
but  little  loss  is  experienced  by  the  nitrogenous 
compounds ;  if  the  mass  is  kept  tightly  pressed  and 
moist  enough  to  exclude  air,  there  will  be  no  loss 
of  fertilising  constituents,  only  a  gradual  decline  of 
weight  as  some  of  the  carbon  compounds  are  con- 
verted into  gases.  Of  course,  as  the  manure  gets 
older  and  shorter  it  becomes  richer  in  nitrogen ;  this 
apparent  increase  is,  however,  simply  due  to  the  loss  of 
non-nitrogenous  carbon  compounds,  whence  it  follows 
that  the  nitrogen,  which  does  not  waste,  always  bulks 
larger  and  larger  in  the  residue.  But  though  there  is 
no  loss  in  nitrogen  in  these  later  stages,  the  more  active 
compounds,  such  as  ammonia  and  the  easily  decom- 
posable amides,  become  converted  by  bacterial  action 
into  carbon  compounds  which  take  longer  to  reach  the 
plant  when  the  manure  finally  gets  in  the  soil. 

Thus,  during  the  making  and  storage  of  farmyard 
manure  there  are  a  large  variety  of  bacterial  actions 
at  work,  some  running  in  an  opposite  sense  to  others, 
and  it  will  depend  on  such  external  conditions  as  the 


S\\:\CHEM1CAL  CHANGES  DURING  DUNG-MAKING  191 

supply  of  air  and  water  which  class  of  action  pre- 
dominates at  any  given  time.  Putrefactive  bacteria  are 
resolving  proteins  into  simpler  compounds  of  nitrogen 
and  ultimately  into  ammonia  ;  oxidising  bacteria  (some- 
times called  denitrifying  bacteria)  set  free  nitrogen 
gas ;  meantime  the  bacteria  engaged  in  the  destruction 
of  cellulose  and  the  formation  of  humus  are  always 
building  proteins  or  bodies  akin  to  them  out  of  the 
previously  produced  amides  and  ammonia. 

One  other  change  sometimes  takes  place  when  the 
manure  is  allowed  to  get  too  loose  and  dry — instead  of 
bacteria,  fungi  begin  to  develop  very  rapidly  until  the 
whole  mass  becomes  permeated  with  the  mycelium. 
The  masses  of  manure  begin  to  look  white  and  dusty, 
a  condition  which  the  practical  man  describes  as  "  fire 
fanged."  It  is  generally  agreed  that  such  manure  is 
seriously  deteriorated,  but  no  analyses  are  available. 

With  these  general  facts  in  mind  it  will  be  possible 
to  interpret  the  experiments  which  have  been  made  to 
ascertain  what  part  of  the  fertilising  materials  contained 
in  foods  consumed  by  animals  is  recovered  in  the  dung 
and  what  losses  occur  during  the  making  and  storage  of 
farmyard  manure.  In  the  first  place,  it  can  be  shown 
that  there  is  no  loss  of  nitrogen  in  the  gaseous  form  due 
to  the  animal ;  the  nitrogen  contained  in  the  urine  and 
faeces  is  equal  to  the  nitrogen  in  the  food,  less  whatever 
may  have  been  retained  by  the  animal  in  its  bodily 
increase.  Numerous  feeding  experiments  demonstrate 
this  point ;  the  following  example  from  Kellner's 
researches  may  be  taken  as  an  illustration. 

An  ox  was  fed  on  a  daily  ration  of  2  kg.  of  gluten 
meal,  2  kg.  of  starch  meal,  4  kg.  of  dried  sugar-beet 
slices,  5  kg.  of  hay,  and  i  kg.  of  chaff,  containing  in  all 
388-8  grms.  of  nitrogen.  About  18-5  kg.  of  dung  was 
excreted  containing  15-36  per  cent  of  dry  matter  and 


192  FARMYARD  MANURE  [chaP. 

100-9  grms.  of  nitrogen,  and  about  13  kg.  of  urine 
containing  2-03  per  cent,  of  nitrogen,  equal  to  265-5 
grms,  of  nitrogen.  The  ox  was  putting  on  weight,  and 
retained  from  the  food  714-5  grms.  of  carbon  and  22-5 
grms.  of  nitrogen.  Thus  of  the  nitrogen  supplied  68-2 
per  cent,  was  excreted  in  the  urine,  25-4  per  cent  in  the 
faeces,  and  about  6  per  cent,  was  retained  by  the  animal. 
To  attain  such  a  result,  however,  it  is  necessary  to 
collect  the  urine  and  fseces  as  they  are  voided,  and  to 
preserve  them  or  analyse  them  before  any  fermentation 
and  evaporation  of  ammonia  can  take  place. 

Assuming  the  animal  itself  to  cause  no  loss  of 
nitrogen  other  than  that  retained  in  the  increased  live 
weight,  a  number  of  experiments  have  been  made  to 
ascertain  the  losses  in  making  farmyard  manure  under 
ordinary  working  conditions. 

For  example,  Maercker  and  Schneidewind,  at  Leuch- 
stadt,  in  1896-7  tied  up  twenty-four  three-year-old 
steers  from  i6th  June  to  29th  October  1896 — 136  days 
— during  which  their  average  increase  of  live  weight 
was  306  lb.  The  food  consisted  of  lucerne  hay,  chaff, 
barley  straw,  dried  sugar  beet  pulp,  decorticated  cotton 
cake,  and  bran,  and  they  were  littered  on  wheat  straw. 

Twelve  of  the  beasts  were  tied  up  in  a  deep,  carefully 
cemented  box  or  pit,  from  which  no  losses  by  drainage 
could  take  place,  and  the  dung  was  not  disturbed  but 
kept  trampled  down  until  the  end  of  the  trial.  The 
second  twelve  were  fed  in  an  ordinary  stall,  and  the 
dung  and  litter  were  removed  every  other  day  to  one 
or  other  of  two  heaps  in  the  yard  alternately,  one  of 
these  being  covered  by  a  roof,  and  the  other  open  to  the 
weather.  At  the  end  of  the  feeding  experiment  the 
three  lots  of  dung  were  carefully  sampled  and  analysed, 
with  the  results  set  out  in  Table  LIV.  below. 

In  a  second  experiment,  fourteen  steers  were  fed  in 


VII.] 


LOSS  OF  NITROGEN 


193 


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194  FARM  YARD  MANURE  [chap. 

the  deep  pit  from  6th  November  1896  to  21st  February 
1897,  when  the  dung  made  was  cleared  out,  sampled, 
and  analysed.  The  experiment  was  then  resumed  until 
2 1st  May,  after  which  the  dung  was  left  in  the  box  for 
another  month,  until  17th  to  i8th  June,  without  any 
beasts  to  keep  it  trodden  down,  the  weather  being 
meantime  very  hot.  The  results  appear  under  items  4 
and  5  in  Table  LIV.  It  will  be  seen  from  this  that  the 
loss  of  nitrogen  was  much  greater  during  the  second 
series,  which  only  differed  from  the  first  in  the  fact  that 
the  dung  lay  without  trampling  for  a  month  during  the 
summer. 

Taking  these  results  as  a  whole,  it  is  seen  that,  even 
with  the  most  careful  management,  the  loss  in  making 
the  dung  amounts  to  13  per  cent,  of  the  total  nitrogen 
supplied  in  the  food,  in  addition  to  6  per  cent,  or  so 
which  the  animals  retain.  This  loss  increases  with 
great  rapidity  if  the  conditions  are  less  favourable ;  the 
minimum  is  only  attained  if  the  dung  be  kept  trampled 
beneath  the  animals  in  a  deep  box,  for  if  it  be  left  to 
itself  for  a  time,  or  if  it  be  made  in  a  shallow  stall  and 
thrown  out  daily  into  a  heap,  as  is  often  the  practice, 
the  loss  rises  to  between  30  and  40  per  cent. 

In  connection  with  the  first-mentioned  experiment, 
Maercker  and  Schneidewind  made  determinations  of 
the  state  in  which  the  nitrogen  exists  in  the  dung, 
whether  it  was  soluble  and  therefore  active,  or  msoluble 
and  comparatively  inactive.  From  the  known  digesti- 
bility of  the  foods  consumed,  it  was  possible  to  calculate 
what  proportion  of  the  nitrogen  in  each  food  left  the 
body  in  a  digested  condition  as  urea  and  kindred 
bodies  dissolved  in  the  urine,  and  what  proportion 
consisted  of  undigested  and  insoluble  compounds  in 
the  faeces.  Maercker  and  Schneidewind  found  not  only 
that  the  loss  had  fallen  upon  the  active  nitrogen — i.e.t 


VII.]  LOSSES  DURING  DUNG-MAKING  195 

that  urea  had  been  transformed  into  ammonium 
carbonate  and  volatilised,  or  broken  up  with  loss  of 
free  nitrogen — but  also  that  some  of  the  active  nitrogen 
had  been  converted  into  an  insoluble  form,  as  though 
the  bacteria  swarming  in  the  dung  had  seized  upon  the 
active  nitrogen  and  converted  it  into  the  insoluble 
material  of  their  own  substance.  Of  course,  this  with- 
drawal of  nitrogen  from  the  active  into  the  insoluble 
form  still  further  reduces  the  value  of  the  dung  as  a 
whole. 

In  France,  experiments  were  carried  out  on  the 
same  question  by  MM.  Miintz  and  Girard,  with 
omnibus  horses,  cows,  and  sheep.  They  showed  that 
with  horses  and  milking  cows,  where  the  manure  was 
removed  every  day,  the  loss  of  nitrogen  amounted  to 
from  30  to  35  per  cent,  of  the  total  nitrogen  contained 
in  the  food.  With  sheep  the  losses  were  still  higher. 
Liberal  littering  and  immediate  treading  of  the  excreta 
into  it  by  the  animal  greatly  reduced  this  loss.  The 
results  are  given  in  Table  LV,  It  is  apparent  that,  on 
the  whole,  the  proportion  of  the  nitrogen  recovered  in 
the  manure  is  about  one-half  of  that  supplied  in  the  food. 

Further  experiments  with  sheep  show  that  the  loss 
was  greatest  with  no  litter,  and  could  be  reduced  by 
using  an  excess,  or  particularly  by  using  peat  moss  or 
earth. 

Loss 
per  cent, 

(No  Litter  .        .  590 

Litter.        .        .  50-2 
T    ■  i 

Litter.        .        .  44-2  f On  Straw        .     50-2 

Abundant  Litter  40-8     !    i5heep.|  ^^   ^^^^^^        ^    ■> 

Experiments  of  the  same  kind  have  also  been 
carried  out  on  the  farm  of  the  Royal  Agricultural 
Society  at  Woburn  for  some  years,  and  the  results 
obtained  in  1899,  1900,  and  1901,  are  given  in  Table  LVI. 


Loss 
per  ceut. 

Horses!^"  S^^^^       •    58o 


Peat  Moss    44-1 


1 96 


FARMYARD  MANURE 


[chap. 


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VII.] 


LOSS  OF  NITROGEN 


197 


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198 


FARMYARD  MANURE 


[chap. 


The  animals  were  fed  in  deep  boxes  with  cemented 
bottoms  and  sides,  and  tlie  dung  was  not  removed 
until  the  feeding  experiment  had  concluded ;  it  was  then 
weighed  and  samples  taken  for  analysis.  The  manure 
was  then,  in  the  early  winter,  made  up  in  a  heap  in  the 
open  on  ground  beaten  down  hard  and  covered 
thoroughly  with  earth.  No  liquid  appeared  to  drain 
away,  and  in  the  spring  the  heap  was  again  weighed 
and  sampled  before  application  to  the  land  for  the  root 
crop.  Here,  again,  the  loss  of  nitrogen  in  making  the 
dung  under  the  best  conditions  varied  from  13  to  18 
per  cent,  while  the  making  into  a  heap  and  storage 
brought  up  the  loss  to  33-37  per  cent. 

Wood,  at  Cambridge,  has  also  estimated  the  losses 
involved   during   the  making  and  storage  of  farmyard 

Table  LVII.— Loss  of  Nitrogen  in  making  Manure  (Wood). 


Retained 

by 

Animal. 

Lost. 

Recovered  in 
Dung. 

During 
Making. 

During 

Storage. 

When 
Made. 

After 
Storage. 

DRY  MATTER. 

Roots  and  Hay  only 
Roots  and  Hay  with  Cake 

2-6 
5-0 

38-8 
35-0 

l6-2 

18.6 

58-6 
6o-o 

42-4 
41-4 

nitrogen. 

Roots  and  Hay  only 
Roots  and  Hay  with  Cake 

8-0 
9-0 

16-8 
12-5 

IO-6 
26-9 

75-2 
78-5 

64-6 
51-6 

manure.  In  his  experiments  four  heifers  were  tied  up 
and  fed,  one  pair  on  mangolds,  hay,  and  straw  alone, 
the  other  pair  on  the  same  foods  with  the  addition  of 
decorticated    cotton   cake.     The    feeding   went   on  for 


vilI 


LOSSES  DURING  DUNG-MAKING 


199 


84  days  in  boxes  with  well-rammed  clay  floors,  the 
dung  was  not  disturbed  but  was  kept  trampled  down  by 
the  animals;  this  is  taken  as  the  period  of  "making" 
the  dung,  and  at  the  end  samples  were  drawn  by  cutting 
out  sections.  The  dung  was  now  left  without  moving 
for  six  months,  May  to  November,  and  again  sampled 
as  it  was  taken  out — this  constitutes  the  storage  period. 
Table  LVII.  shows  the  fate  of  100  lb.  of  dry  matter  and 
nitrogen  respectively  fed  to  the  animals. 

In  an  experiment  made  by  Russell  and  Goodwin 
at  the  Wye  Agricultural  College,  the  beasts  were  fed 
upon  roots,  hay,  and  linseed  cake,  a  comparison  being 
made  between  linseed  cake  poor  and  rich  in  oil  respec- 
tively. The  feeding  lasted  for  twelve  weeks  and  the  litter 
was  composed  of  a  bottom  layer  of  peat  moss,  to  which 
straw  was  added  at  the  rate  of  28  lb.  per  week.  Table 
LVII  I.  shows  the  results  obtained. 


Table  LVIII.- 

-Loss 

OF  Nitrogen 

IN  MAKING  Manure 

(Russell). 

Nitrogen  supplied. 

Nitrogen 
recovered. 

Nitrogen 
lost. 

|3 

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Lb.        Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

I. 

Cake  poor  in 

Oil  . 

43-83 

11-77    4-35 

3-07 

28-6 

20-9 

7-38 

14-9 

2. 

Cake  rich  in 

Oil    . 

33-29 

10-19    4-35 

2-04 

22-1 

i6-  9 

6.69 

14.4 

The  dung  was  sampled  immediately  the  experiment 
was  over,  while  the  manure  was  still  tight  under  the 
feet  of  the  animals  ;  the  experiment  also  took  place 
during  the  winter  months,  yet  the  loss  still  amounted 
to  nearly  15  per  cent,  of  the  total  nitrogen.  It  is  note- 
worthy that  all  the  experiments  quoted  show  practically 
this  same  loss   of   15   per  cent,  for  the  first  stage   of 


200  FARMYARD  MANURE  [CHAP. 

the  dung-making  process  under  the  best  conditions. 
Not  only  does  the  loss  fall  upon  the  active  compounds 
of  nitrogen,  but  a  still  further  amount  is  converted 
into  more  slowly  acting  bodies.  For  example, 
in  experiment  i  there  were  43-83  lb.  of  digestible 
nitrogen  fed,  of  which  the  animal  only  retained  3-07  ; 
the  remainder,  40-76  lb.,  was  excreted  as  urea,  but  only 
28-6  lb.  of  ammoniacal  and  amide  nitrogen  were  found 
in  the  dung,  so  that  besides  the  loss  of  7-38  lb.  another 
4-78  lb.  had  been  transformed  into  proteins  and  other 
insoluble  compounds. 

It  will  be  seen  that  in  all  cases  the  losses  fall  most 
heavily  on  the  rich  dung  made  by  animals  receiving 
concentrated  foods ;  they  also  fall  almost  entirely  on 
the  most  valuable  part  of  the  manure — the  urea  and 
ammonia  compounds  arising  from  the  digestible  por- 
tions of  the  food.  It  is  also  clear  that  these  losses  are 
avoided  when  the  food  is  consumed  upon  the  land,  as 
by  sheep  folded  on  the  arable,  milch  cows  grazing  or 
beasts  fattened  with  cake  upon  the  summer  grass. 

Of  course,  in  all  these  considerations  no  account  has 
been  taken  of  such  preventable  losses  as  those  which 
too  often  occur  through  the  escape  of  the  liquid  portions 
of  the  manure  in  a  leaky  yard  or  into  the  drains, 
or  by  the  washing  of  rain  through  the  dung  heap.  Such 
losses  are  very  great  and  fall  on  the  most  valuable 
substances  in  the  manure — the  soluble  ammonia  and 
potash  compounds  which  occur  in  the  liquid  portion. 

In  order  to  minimise  these  losses  of  nitrogen,  a 
number  of  substances  have  been  suggested,  which,  when 
strewn  about  the  cattle  stalls  and  mixed  with  the  fresh 
dung,  would  either  combine  with  the  ammonia  and 
prevent  its  volatilisation,  or  by  reducing  the  bacterial 
actions  would  hinder  its  formation.  These  preserva- 
tives  fall  into  two   classes :  those  designed  merely  to 


VII.]  PRESER  VA  TIVES  IN  D  UNG-MAKING  201 

fix  the  ammonia,  and  the  true  antiseptics  which  will 
check  the  production  of  either  ammonia  or  free  nitro- 
gen gas.  Of  the  first  class  of  substances,  the  oldest 
proposal  was  to  use  gypsum,  which  would  react  with 
the  ammonium  carbonate  and  form  the  non-volatile 
ammonium  sulphate. 

(NH4)2C03  +  CaS04,  2H2O  =  (NH4)2S04-l-CaC03+ 2H2O. 

The  drawback  to  the  use  of  gypsum  lies  in  the  large 
quantities  that  are  required ;  the  reaction  represented 
by  the  above  equation  is  really  a  reversible  one,  so 
that  only  part  of  the  ammonium  carbonate  is  trans- 
formed into  sulphate,  the  amount  being  proportional 
to  the  excess  of  gypsum  present.  As  also  the  gypsum 
is  an  insoluble  salt,  far  more  than  the  calculated  quan- 
tity will  be  required  for  an  efficient  fixation  of  the 
ammonia.  Again,  the  urine  contains  nearly  all  its 
potash  in  the  form  of  potassium  carbonate,  and  this 
also  will  react  with  gypsum,  increasing  the  quantity 
that  must  be  used  before  the  ammonia  is  fixed. 

From  the  above  equation,  about  1 1  lb.  of  gypsum 
would  be  required  for  each  ton  of  dung,  but  at  least 
ten  times  as  much  as  this  would  be  necessary  in  practice, 
or  a  hundredweight  of  gypsum,  costing  2s.  for 
each  ton  of  farmyard  manure  made.  Besides  the 
question  of  cost,  another  great  drawback  to  the  use 
of  gypsum  lies  in  the  fact  that  the  calcium  sulphate 
is  itself  liable  to  bacterial  change ;  during  the  storage 
of  the  dung  it  is  reduced  by  anaerobic  bacteria  to  the 
state  of  calcium  sulphide,  which  afterwards  acts  injuri- 
ously on  plant  life  when  the  farmyard  manure  is 
applied  to  the  soil. 

Another  suggestion  has  been  to  use  kainit,  because 
it  is  composed  of  salts  of  magnesium  and  potassium 
which   will   to   a  certain   extent   be   transformed  intp 


202  FARMYARD  MANURE  [chap. 

carbonates  and  fix  the  ammonia  as  chloride  or  sulphate. 
Here,  again,  the  quantity  required  is  very  large,  though 
the  soluble  nature  of  the  kainit  enables  it  to  be  utilised 
more  thoroughly.  But  of  this  class  of  substances  the 
most  effective  is  superphosphate ;  the  acid  calcium 
phosphate  it  contains  reacts  with  the  ammonium  car- 
bonate to  form  a  double  ammonium  calcium  salt, 
insoluble  indeed,  but  readily  becoming  available  for 
the  plant.  The  same  objections,  however,  apply  to 
superphosphate  as  to  gypsum  ;  uneconomical  quantities 
are  required  if  the  fixation  of  the  ammonia  is  to  be 
complete,  the  superphosphate  itself  contains  gypsum 
which  becomes  reduced  to  the  injurious  calcium  sul- 
phide, and  again  the  acid  superphosphate  is  found  to 
be  harmful  to  the  feet  of  the  animals  treading  down 
the  litter  among  which  it  is  strewn. 

Sulphuric  acid  itself  has  been  tried,  as  also  peat 
moss  impregnated  with  small  quantities  of  the  same 
acid,  but  neither  have  proved  successful  for  the  reasons 
indicated  above. 

As  to  antiseptics  proper,  soluble  fluorides  and  even 
carbon  bi-sulphide  have  been  tried,  but  the  saving 
effected  in  the  nitrogen  is  never  sufficient  to  pay  for 
the  cost  of  the  material  and  the  trouble  of  applying 
it.  Schneidewind,  in  the  course  of  his  experiments  at 
Leuchstadt,  found  that  the  only  practical  means  of 
reducing  the  losses  of  nitrogen,  was  to  place  a  layer 
of  old  well-rotted  farmyard  manure  as  a  basis  for  the 
new  manure  heap ;  this  had  a  distinctly  beneficial  effect 
and  always  resulted  in  smaller  losses  of  nitrogen, 
probably  because  of  the  constant  evolution  of  carbonic 
acid  from  the  layer  of  old  manure. 

Turning  now  to  the  composition  of  farmyard  manure, 
the  average  of  a  large  number  of  analyses  at  Rotham- 
sted  shows  that  it  contains  about  three-quarters  of  its 


VII.]     COMPOSITION  OF  FARMYARD  MANURE        203 


weight  of  water,  about  two-thirds  of  i  per  cent,  of 
nitrogen,  one-quarter  of  i  per  cent,  of  phosphoric  acid, 
and  one-third  of  i  per  cent,  of  potash,  or  per  ton  about 
15  lb.  of  nitrogen,  5  lb.  of  phosphoric  acid,  and  7  lb. 
of  potash.  The  composition,  however,  will  vary  very 
greatly,  both  with  the  nature  and  feeding  of  the  animals, 
and  the  treatment  and  storage  the  manure  receives. 

The  influence  of  the   feeding  is  well  illustrated  in 
a   series   of  analyses   of  two    lots   of   dung,  made    in 

Table    LIX.— Percentage   Composition   of   Farmyard   Manure 

MADE     at     RoTHAMSTED     FROM      ROOTS     AND     HaY     ONLY,     OR 

FROM   Roots  and  Hay  with  Cake. 


;S 

if 

g   .a 

|«  5 
■c    a 

as 

II 

.2  a 

1904 

23-6 

0-577 

0-046 

0-067 

0-464 

1904 

24-03 

0-716 

0-079 

0-096 

0-541 

1905 

29.5 

0-462 

0-040 

0-047 

0-375 

1905 

31-3 

0-698 

0-182 

0-055 

0-461 

1906 

22-0 

0-466 

0-022 

0-033 

0-411 

1906 

24-3 

0-690 

0-097 

0-049 

0-544 

1907 

25-3 

0-589 

0-125 

0-053 

0-411 

1907 

25-5 

0-815 

0-377 

0033 

0-405 

Roots  and  Hay 

only    , 
Cake-fed 

Roots  and  Hay 

only    . 
Cake-fed 

Roots  and  Hay 
only    .         . 
Cake-fed 

Roots  and  Hay 

only    . 
Cake-fed 


(Made  into 
Mixen  and 
stored. 


Do. 


Do. 


Not 
stored. 


adjoining  boxes  by  bullocks  receiving  in  the  one  case 
roots  and  hay  only,  and  in  the  other  a  fattening  ration 
of  cake  in  addition  to  the  roots  and  hay.  The  two  lots 
of  dung  were  generally  made  up  into  separate  mixens 
out  of  doors,  and  sampled  a  month  or  two  later,  when 
they  were  carted  out  to  the  land  ;  in  one  case  they 
were  sampled  as  they  left  the  boxes.  Table  LIX. 
shows  the  analytical  results,  not  only  as  regards  the 


204 


FARMYARD  MANURE 


[chap. 


total  nitrogen,  but  also  that  present  as  salts  of  ammonia, 
and  as  amido-compounds  easily  changing  into  ammonia 
It  will  be  seen  that  the  cake-fed  dung  is  always 
considerably  richer  in  nitrogen,  the  average  percentage 
being  0-73  as  against  0-523,  a  superiority  of  nearly  40 
per  cent.  Moreover,  the  extra  nitrogen  in  the  cake- 
fed  dung  is  mostly  in  the  highly  available  forms,  the 
ammonia,  urea,  and  amido-compounds  which  represent 
the  digestible  nitrogen  of  the  cake ;  the  insoluble  nitro- 
Table  LX.— Crop  Returns  from  the  above  Manures. 


Year  of 
Application. 

Second 
Tear. 

Third 
Year. 

Mean  of  4. 

Mean  of  4. 

Mean  of  3. 

Unmanured  Plot       .... 
16  tons  per  acre  Root  and  Hay  Dung 
16  tons  per  acre  Cake-fed  Dung 

lOO 
132 
183 

100 
131 
137 

100 
112 

118 

gen  in  the  cake-fed  dung  is  only  0-488,  as  against  0-415 
in  the  dung  made  from  roots  and  hay,  a  superiority  of 
less  than  18  per  cent.  That  the  superiority  of  the 
cake-fed  dung  as  regards  the  soluble  nitrogen  com- 
pounds is  not  even  more  pronounced,  is  due  to  the 
change  back  from  ammonia  into  proteins  effected  by 
bacteria  during  storage ;  in  1907,  when  the  dung  was 
sampled  as  it  left  the  yard,  both  lots  contained  practically 
the  same  proportion  of  insoluble  nitrogen,  and  both  pos- 
sessed an  exceptional  amount  of  ammonia,  which,  how- 
ever, was  three  times  as  much  in  the  cake-fed  as  in  the 
other  manure.  These  differences  in  composition  are 
clearly  reflected  in  the  crops  grown  with  equal  quan- 
tities of  the  two  manures,  the  weights  of  which  are 
summarised  and  reduced  to  a  common  standard  (the 
yield  of  the  unmanured  plots  being  taken  as  100)  in 
Table    LX.      The    crops   grown   in   these  trials   were 


Vii.]       VARIABLE  COMPOSITION  OF  MANURE         205 

Swedes,  barley,  mangolds,  and  wheat  in  rotation,  and 
after  the  two  kinds  of  dung  had  been  applied  in  a  given 
year,  no  other  manure  was  used  on  those  plots  for  the 
next  three  years.  In  the  first  year  the  increase  in 
yield  produced  by  the  cake-fed  dung  was  83  per  cent., 
as  compared  with  an  increase  of  32  per  cent,  produced 
by  the  root  and  hay  dung ;  in  the  following  year  the 
residue  left  by  the  cake-fed  dung  produced  an  increase 
of  37  per  cent.,  as  against  31  per  cent,  from  the  residue 
of  the  other  manure ;  in  the  third  year  the  increases 
produced  by  the  residues  still  remaining  were  18  and 
12  per  cent,  respectively.  The  great  difference  in  the 
value  of  the  two  manures  comes  in  the  first  year,  for 
though  the  superiority  of  the  cake-fed  dung  may  still 
be  seen  in  the  second  and  third  year,  it  is  almost  covered 
by  the  experimental  error. 

The  analyses  in  Table  LXI.  show  the  change  in 
composition  which  results  from  the  storage  of  farmyard 

Table  LXI. — Composition  of  Farmyard  Manure  from 

VARIOUS  SOURCES. 


Water. 

Nitrogen. 

Phosphoric 
Acid. 

Potash. 

I.  Fresh  long  Straw 

66.I7 

0-544 

0.318 

0-673 

2.  No.  I  after  rotting 

75-4 

0-597 

0-454 

0-491 

3.  Very  old  and  short  from  a 

mushroom  bed  . 

53-14 

0'8o 

0-63 

0-67 

6.  Very  old  J            "^^^^           \ 

75-0 

0-39 

o-l8 

0-45 

75-0 

0-50 

0-26 

0-53 

79-0 

0-58 

0-30 

0-50 

7.  Rothamsted  average    . 

76-0 

0-64 

0*23 

0-32 

8.  Fresh  Liquid  Manure  . 

98-02 

0-044 

0-051 

0-355 

9.  Old 

99-13 

0-026 

0-0x4 

0-22 

manure ;  it  will  be  seen  that  old  short  dung  contains  a 
higher  proportion  of  fertilising  constituents  (z>.,  when 
reckoned  in  the  dry  matter,  because  the  amount  of 
water  present   at   any  time   is  a   matter   of  accident) 


2o6  FARMYARD  MANURE  [chap. 

than  fresh  dung,  if  it  has  been  at  all  properly  managed. 
We  have  already  seen  that  though  considerable  losses 
of  nitrogen  take  place  during  the  rotting  down  of  the 
manure,  the  losses  of  non-nitrogenous  organic  matter 
are  greater  still,  so  that  the  manure  becomes  concen- 
trated in  nitrogen  and  still  more  so  in  phosphoric  acid 
and  potash.  The  active  compounds  of  nitrogen,  how- 
ever, like  ammonium  carbonate,  grow  less  as  the  manure 
ages,  since  they  are  constantly  being  converted  into 
insoluble  protein-like  bodies  making  up  the  bacteria 
themselves.  These  of  course,  die  and  decay,  giving 
rise  again  to  soluble  nitrogenous  compounds,  but  the 
tendency  is  on  the  whole  in  the  other  direction,  so  that 
the  older  the  manure  the  poorer  it  becomes  in  ammonia 
and  kindred  bodies.  Hence  old  short  dung  is  both 
slower  in  its  action  and  less  caustic  to  germinating 
seedlings  or  the  fresh  delicate  rootlets  of  tender  plants ; 
it  can  in  consequence  be  used  with  more  safety  in  the 
spring  in  potato  drills  or  immediately  beneath  the  seeds 
of  Swedes  and  mangolds,  particularly  on  a  light  soil.  A 
few  analyses  of  liquid  manure  are  also  given,  though  it 
is  subject  to  such  variations  in  the  amount  of  rain-water 
that  gets  mixed  with  it  and  the  degree  to  which  its 
■constituents  are  held  back  by  the  litter,  that  little  can 
be  deduced  from  these  results  as  to  the  composition  of 
any  other  sample.  It  will  be  seen,  however,  that  the 
fertilising  constituents  are  chiefly  nitrogen  and  potash, 
both  in  an  active  form  ;  hence  it  forms  a  very  valuable 
manure  for  grass  land. 

Table  LXII.  shows  a  series  of  analyses  made  by  B. 
Dyer  of  stable  manure  from  London,  such  as  is  used  in 
very  large  quantities  by  farmers  and  market  gardeners, 
whose  distance  from  London  does  not  render  the  freight 
too  great.  The  most  noticeable  thing  in  the  five  last 
analyses  is  the  very  low  proportion   of  nitrogen   that 


VII.]  COMPOSITION  OF  LONDON  STABLE  MANURE  207 


remains  soluble ;  the  frequency  with  which  the  stables 
are  cleaned  out  in  London,  the  open  nature  of  the 
heaps,  and  the  many  turnings  to  which  the  manure  is 
subjected  in  collection  and  transit,  all  result  in  extreme 
aeration  and  a  rapid  fermentation  with  a  corresponding 
loss  of  ammonia.  The  last  three  samples  had  been 
stored  for  eight  or  nine  months  on  the  farm  ;  usually  no 
great  care  is  taken  to  consolidate  such  heaps,  so  that  the 

Table  LXIL— Composition  of  London  Stable  Manure 
(B.  Dyer). 


Peat 
Moss. 

Straw. 

Mixed  Peat  Moss  and  Straw. 

Fresh. 

After  Storage. 

1 

2 

1 

2 

3 

Water    . 
Organic  Matter 
Nitrogen,  soluble  . 
Nitrogen,  insoluble 
Phosphoric  Acid    ■ 
Potash  . 

77.8 
i8-o 
o-Si 
0-37 
0.37 
102 

70-0 
24-3 

O-IO 

0-52 
0-48 
0.59 

76.1 

19-3 
o-o8 
0-46 
0-33 
0-45 

62 -0 
26.4 
o-oS 
0-62 
0.45 
0-58 

53-8 

17-5 
0'06 
0-58 
0.49 
0-58 

6i'9 
22 -o 
o-o8 
0.68 
0-56 
0.65 

52-9 

23-0 
O-IO 

0-79 
0-66 
o-8o 

rotting  down  process  goes  on  rapidly.  In  the  above 
cases  Dr  Dyer  calculates  that  the  loss  in  organic  matter 
had  been  about  40  per  cent,  and  in  nitrogen  from  15 
to  20  per  cent,  during  the  storage. 

From  a  consideration  of  the  origin  of  the  losses  of 
nitrogen  which  take  place  during  the  making  of  dung, 
and  of  the  above  analyses,  a  good  deal  of  guidance  can 
be  obtained  as  to  the  practical  management  of  farmyard 
manure,  which  remains  the  fundamental  fertiliser  in  the 
ordinary  course  of  farming  in  this  country.  In  the  first 
place,  since  it  is  clear  that  the  most  valuable  part  of  the 
manure  resides  in  the  liquid,  far  more  care  should  be 
taken  to  preserve  this  than  is  usually  the  case.  Whether 
the  dung  is  made  in  boxes  or  in  yards,  there  should  be 


2o8  FARMYARD  MANURE  [chap. 

sufficient  depth  to  allow  the  manure  to  accumulate 
under  the  animal  for  the  whole  winter  if  need  be,  and 
the  floors  should  be  rammed  with  clay  to  render  them 
water-tight.  Yards,  in  particular,  should  be  constructed 
so  that  the  accumulated  manure  is  not  above  the  general 
ground  line  outside,  in  which  case  there  will  always  be 
a  gradual  soaking  away  of  the  liquid.  On  the  other 
hand,  yards  made  thus  below  the  general  ground  level 
are  apt  to  flood  in  heavy  rain,  so  that  the  excess  of 
liquid  containing  the  soluble  part  of  the  manure  has  to 
be  run  off  to  waste  by  means  of  a  drain ;  this  can, 
however,  be  avoided  by  cutting  drains  outside  to  keep 
land  water  from  running  into  the  yard,  and  by  seeing 
that  all  the  surrounding  sheds  are  properly  provided 
with  guttering.  For  real  economy  of  litter,  part  at  least 
of  the  yard  should  be  covered  ;  if  the  whole  yard  is 
covered  a  certain  amount  of  care  is  necessary  to  prevent 
the  dung  from  getting  at  times  too  dry.  Only  just 
enough  litter  should  be  used  to  soak  up  the  urine,  and 
in  order  to  prevent  the  liquid  working  up  to  the  surface 
with  the  trampling,  the  floor  of  the  yard  should  run 
down  to  a  slight  hollow,  filled  at  first  with  something 
stiff  like  bean  haulm  or  coarse  peat  moss,  in  which  the 
excess  of  liquid  may  collect.  Above  all,  the  manure 
should  be  kept  tightly  trampled  ;  the  greatest  amount  of 
loss  takes  place  when  the  urine  falls  on  a  thin  layer  of 
loose  strawy  litter.  The  yards  and  boxes  should  be 
deep  enough  to  carry  the  animals  through  the  whole 
winter,  so  that  they  need  not  be  cleaned  out  except 
when  dung  is  wanted  to  go  straight  on  the  land.  A 
box,  for  example,  8  ft.  by  lo  ft.  in  area,  with  an  avail- 
able depth  of  3  ft.  would  hold  about  9  cubic  yards,  or  8 
tons  of  dung  when  well  trodden  down.  This  would 
accommodate  two  beasts,  each  receiving  10  lb.  of  straw 
in  food  and  12  lb.  in  litter  per  diem,  for  four  months. 


VII.]     MANAGEMENT  OF  FARMYARD  MANURE      209 

As  far  as  possible  manure  made  in  the  spring  should 
be  left  undisturbed  until  the  autumn,  it  may  then  be 
carted  out  on  to  the  stubbles  and  ploughed  in  where 
potatoes  or  roots  are  to  be  taken  in  the  following 
spring.  Even  on  the  lightest  soils  the  land  will  be 
more  benefited  thus  than  if  the  manure  is  made  up 
into  a  mixen  and  only  put  on  immediately  before  the 
roots  are  grown.  Sometimes,  of  course,  a  potato  grower 
must  have  a  supply  of  well-rotted  manure  to  put  in  the 
drills  immediately  before  planting ;  this  can  often  be 
got  from  the  lower  layers  of  the  earliest  used  boxes  or 
yards,  since  a  mixen  should  be  avoided  as  much  as 
possible.  The  principle  to  keep  in  mind  is  that  every 
disturbance  of  farmyard  manure  results  in  loss,  and  that 
the  shorter  the  time  which  elapses  between  the  dropping 
of  the  dung  and  its  application  to  the  land,  the  less  this 
loss  of  fertilising  material  will  become. 

In  considering  the  value  of  farmyard  manure  as  a 
fertiliser  one  has  to  keep  in  mind  that  it  is  an  essential 
product  of  the  farm,  and  that  it  must  constitute  the 
main  source  of  manure  for  the  land  under  the  conditions 
of  ordinary  mixed  farming,  where  artificial  manures  will 
only  be  used  as  supplements  and  not  as  rivals.  It  is 
only  in  certain  special  cases,  such  as  potato  or  hop 
growing,  where  the  ordinary  course  of  farming  does  not 
supply  as  much  farmyard  manure  as  is  wanted,  that  the 
question  has  to  be  decided  whether  artificial  manures 
or  dung  from  the  towns  shall  be  purchased,  or  again 
whether  stock  shall  be  fattened  solely  with  the  view  of 
making  manure. 

As  a  fertiliser,  the  chief  value  of  farmyard  manure 
lies  in  the  fact  that  it  contains  all  the  elements  of  a 
plant's  nutrition — nitrogen,  phosphoric  acid,  and  potash 
— though  for  a  well-balanced  manure  the  phosphoric 
acid  is  comparatively  deficient.     Moreover,  the  nitrogen 

O 


2IO 


FARMYARD  MANURE 


[chap. 


is  present  in  various  forms  of  combination,  varying  from 
the  rapidly  acting  ammonia  compounds  down  to  some 
of  the  undigested  residues  which  will  remain  for  a  very 
long  period  in  the  soil  before  becoming  available  for  the 
plant.  In  consequence  dung  is  a  lasting  manure,  which 
accumulates  in  the  soil  to  build  up  what  a  farmer  calls 
"high  condition" — the  state  of  affairs  which  prevails 
when  the  reserves  of  manure  in  the  soil  are  steadily 
and  continuously  passing  into  the  available  condition 
in  sufficient  amount  for  the  needs  of  the  crop,  so  that 
there  is  no  necessity  for  freshly  applied  active  manure 
— a  state  of  affairs  which  results  in  healthy  growth 
and  good  quality.  But  however  marked  the  farmer's 
preference  is  for  such  lasting  manures,  the  delay  in 
realising  the  capital  they  represent  means  a  certain 
amount  of  loss  ;  besides  which,  some  of  the  constituents 
of  farmyard  manure  are  so  slowly  acting  as  to  be  hardly 
recoverable  during  the  lifetime  of  the  tenant.  The 
imperfect  recovery  of  the  nitrogen  from  large  dressings 
of  farmyard    manure   is   illustrated    in    Table  LXIII., 

Table  LXIII. — Mangolds.  Relation  between  the  Nitrogen 
Recovered  in  Crop  and  that  Supplied  in  Manure 
(Rothamsted.) 


Plots. 

Manure. 

2  " 

S  0 
la 

Nitrogen. 

cm 
■"  0 

S30 

a 

2 

■2  ^  a 

.9     S 

Kg 

4N 
4A 
4C 
lO 

Nitrate  of  Soda,  550  lb, 
Ammoiiium  Salts,  400  lb. 
Rape  Cake,  2000  lb. 
Farmyard  Manure,  14  tons 

Tons. 

17-95 
15-12 
20-95 
17-44 

Per 
cent. 
0-164 

0-I45 
0-1^8 
0-162 

Lb. 

67-2 
4Q-3 
69-4 
63-3 

Lb. 

86 

86 

98 

200 

Per 
cent. 
78-1 
57-3 
70-9 
31-6 

Vil]       RECO  VER  V  OF  NITROGEN  IN  MANURE        1 1 1 

which  shows  the  nitrogen  removed  in  the  mangold  crops 
at  Rothamsted  when  grown  with  farmyard  manure  and 
other  sources  of  nitrogen. 

In  this  case  78  per  cent,  of  the  nitrogen  applied  as 
nitrate  of  soda  is  recovered  in  the  crop,  and  71  per  cent. 
of  that  applied  as  rape  cake,  while  only  32  per  cent,  of 
that  which  was  estimated  to  be  included  in  the  dung 
has  come  back  in  the  crop.  This  low  figure  is  partly 
due  to  the  fact  that  the  dung  was  put  on  year  after  year 
in  considerable  quantities  (14  tons  per  acre) ;  hence  all 

Table  LXIV.— Fate  of  Nitrogen  in  Farmyard  Manure, 
APPLIED  TO  Wheat  (Rothamsted). 


Plot. 

Manuring. 

Nitrogen  in  Soil 

9  inches  deep, 

1S93. 

Approximate 

supply  of  Nitrogen 

in  Manure  in 

50  years. 

Approximate  re- 
moval of  Nitrogen 
in  Crops,  50  years 
(1S44-1S93). 

Surplus  of  Nitrogen 
over  Plot  8, 

unaccounted  for  in 
Crop  or  Soil. 

Per  cent. 

Pounds 
per  acre. 

3 
2 

Unmanured  . 
Farmyard  Manure 

0-0992 

0-2207 

2570 
5150 

Lb. 
10,000 

Lb. 

850 

2600 

Lb. 
5670 

the  wasteful  processes  are  increased  and  there  is  also  a 
great  accumulation  of  nitrogenous  material  in  the  soil. 
How  great  the  waste  may  become  is  seen  by  comparing 
the  nitrogen  supplied  to  one  of  the  permanent  wheat 
plots  at  Rothamsted,  which  receives  14  tons  of  farmyard 
manure  per  acre  every  year,  with  the  nitrogen  stored  up 
in  the  soil  and  that  removed  in  the  crop.  Table  LXIV. 
shows  that  only  26  per  cent,  was  recovered  in  fifty 
years,  and  that  nearly  57  per  cent,  has  been  lost,  since 
it  is  accounted  for  neither  in  the  crop  nor  in  the  soil  at 
the  end  of  the  period. 

These,  however,  are  extreme  cases ;  on  referring  to 
the  crops  grown  with  the  rich  and  poor  dung  on  p.  204, 


2t2  '       P ARM  YARD  MANURE  [chap 

where  four  crops  in  rotation  are  grown  after  each 
application  of  farmyard  manure,  out  of  207  lb.  "of 
nitrogen  supplied  as  dung  made  from  roots  and  hay 
alone  144  lb,  were  recovered  in  the  three  following 
years,  and  of  257  lb,  supplied  as  cake-fed  dung  158  lb. 
were  similarly  recovered. 

The  extremely  lasting  character  of  those  nitrogenous 
compounds  in  farmyard  manure  which  are  not  recovered 
in  the  first  year  is  illustrated  in  an  exceptional  manner 
in  the  Rothamsted  experiments.  On  the  grass  land, 
for  example,  one  plot  received  14  tons  of  dung  per 
acre  per  annum  for  eight  years  (1856-63)  and  then  was 
left  unmanured.  Table  LXV.  shows  that  it  has  con- 
tinued to  give  a  larger  crop  than  the  unmanured  plot 
alongside  for  more  than  forty  years.  The  table  shows 
that  in  the  first  year  after  the  application  of  farmyard 
manure  had  been  stopped  the  plot  with  the  residues  of 
the  previous  eight  years'  manuring  gave  double  the  yield 
of  the  unmanured  plot ;  in  the  following  year  the  yield 
was  still  double ;  but  from  that  time  its  superiority  has 
slowly  declined,  though  for  the  last  ten  years  it  has 
still  amounted  to  1 5  per  cent. 

A  similar  experiment  was  made  on  the  barley  plots, 
one  of  which  received  14  tons  per  acre  of  farmyard 
manure  for  twenty  years  from  1852  to  1871,  and  has 
since  been  left  unmanured.  Table  LXVI.  shows  the 
yield  from  this  plot,  from  the  unmanured  plot,  and  from 
the  plot  which  has  continued  to  receive  14  tons  of 
farmyard  manure  every  year,  for  the  years  immediately 
following  the  discontinuance  of  the  dung  and  for 
successive  five-year  periods  since.  It  will  be  seen 
that  though  the  yield  has  fallen  continuously  to  about 
40  per  cent,  of  that  of  the  continuously  dunged  plot, 
it  still  remains  more  than  double  that  of  the  wholly 
unmanured  plot. 


ni.] 


PRODUCE  OF  HA  V  PER  ACRE 


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214 


FARMYARD  MANURE 


[chap. 


In  considering  the  results  of  these  last  two  experi- 
ments, it  must  be  remembered  that  such  a  long  duration 
of  the  residues  of  farmyard  manure  would  not  be  per- 
ceptible in  practice :  they  only  become  apparent  when 
the  soils  are  cropped  to  a  state  of  exhaustion  that  would 
never  be  met  with  in  ordinary  farming  experience. 

Table  LXVI,— Total  Produce  per  acre  of  Barley  Plots, 
SHOWING  Residual  Effects  of  Dung. 


C3 

2  .1 

•gi? 

►>     6 

>>•-*  * 

fc-^-l 

ofe-g 

ii 

Relation  to  Produce           1 

IM  r-1    £ 

g° 

of  Plot  7-2 

f\ 

reckoned  as  100. 

n 

2     CI 

0 

Q 

p  ^ 

Plot  r-2. 

Plot  7-1. 

Plot  1-0. 

Plot  7-2. 

Plot  7-1. 

Plot  1-0. 

Mean. 

Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

Lb. 

1852-1871 

5933 

2454 

100 

41 

1872 

5202 

4870 

1282 

100 

94 

25 

1873 

6561 

5165 

1570 

100 

79 

24 

1874 

7943 

5675 

1922 

100 

71 

24 

1875 

5825 

3955 

1448 

100 

68 

25 

1876 

6166 

4010 

1561 

ICO 

65 

25 

Mean. 

1877-1881 

6167 

3305 

1528 

TOO 

54 

25 

1882-1886 

6546 

3494 

1529 

100 

53 

23 

1887-1891 

5334 

2664 

1379 

100 

50 

26 

1892-1896 

6477 

3101 

1508 

100 

48 

23 

1897-1901 

5349 

2251 

II41 

100 

42 

21 

1 902- 1 906 

6223 

2485 

1 301 

100 

40 

21 

Since  only  a  portion — and  that  not  the  largest — of  the 
nitrogen  of  farmyard  manure  is  readily  available,  if  it  is 
the  only  manure  supplied  the  crop  in  a  good  season 
is  often  unable  to  obtain  nitrogen  rapidly  enough,  even 
though  very  large  quantities  are  lying  dormant  in  the 
soil.     As   an  example,  we  may  take   the  Rothamsted 


VII.] 


SLOW  AVAILABILITY  OF  MANURE 


215 


mangold  crops  for  the  years  1900  and  1907,  when  crops 
considerably  above  the  average  were  grown,  and  com- 
pare the  yields  obtained  when  farmyard  manure  was 
used  alone,  with  that  given  by  a  purely  artificial  dressing 
containing  nitrate  of  soda  and  by  farmyard  manure 
supplemented  by  nitrate  of  soda  : — 

Table  LXVII.— Yield  of  Mangolds  at  Rothamsted,  1900  and  1907. 
Roots  only. 


Year. 

Farmyard 

Manure 

+PhosphoricAcid 

and  Potasli 

=  200  lb.  N. 

Nitrate  of  Soda 

+  Phosphoric  Acid 

and  Potash 

=  861b.  N. 

Farmyard 

Manure 

=  :;L)0  1b.  N. 

+Nitrat«of  Soda 

=  86  lb.  N. 

Farmyard 

Manure 

=  200  lb.  N. 

+ Nitrate  of  Soda 

+  Phosphoric  Acid 

and  Potash 

=  86  1b.  N. 

1900 
1907 

Tons. 
28-0 
26-5 

Tons. 

33-1 
32-8 

Tons. 

41-3 
41-4 

Tons. 
41-8 

42-1 

The  farmyard  manure,  though  it  contains  about  200 
lb.  of  nitrogen,  cannot  provide  the  rapidly  growing 
mangolds  with  as  much  nitrogen  as  does  the  nitrate  of 
soda  containing  86  lb.  of  nitrogen,  since  it  only  grew 
27-2  tons  of  mangolds  against  33  tons  with  nitrate  of 
soda,  and  this  notwithstanding  the  great  accumulation 
in  the  soil  of  the  residues  of  thirty  years'  previous 
manuring  with  dung.  That  only  the  nitrogen  was 
concerned  in  these  differences  is  seen  from  the  fact 
that  both  the  plots  received  the  same  phosphoric  acid 
and  potasK  The  crop  had  by  no  means  reached  its 
limit,  for  an  addition  of  nitrate  of  soda  to  the  dung 
increased  the  crop  to  41-4  tons  ;  and  here,  again,  only  the 
nitrogen  is  concerned,  because,  on  a  further  plot  where 
phosphoric  acid  and  potash  were  added  to  the  combina- 
tion of  dung  and  nitrate  of  soda,  there  was  but  a  very 
slight  additional  increase  of  crop. 

From   other   experiments   it    has    been   repeatedly 


2i6  FARMYARD  MANURE  [chap. 

demonstrated  that  where  the  grower  is  aiming  at  a  very 
large  crop  it  is  more  economical  to  attain  this  by  using 
dung  and  a  mixture  of  active  artificial  fertilisers  than 
by  increasing  the  amount  of  dung ;  20  loads  of  dung, 
with  I  to  2  cwt.  of  nitrate  of  soda  and  3  cwt,  of  super- 
phosphate costing  about  30s.,  will  generally  be  more 
effective  than  40  loads  of  dung,  of  which  the  second  20 
loads  cannot  be  charged  at  less  than  £a^  or  £^. 

Farmyard  manure  has  frequently  been  blamed  for 
carrying  the  seeds  of  disease  and  of  weeds  which  have 
passed  through  the  animals  making  the  dung  in  an 
unchanged  condition  and  thus  contaminate  the  land  for 
other  crops.  When  bullocks  have  been  fed  with  Swedes 
affected  with  "  finger-and-toe "  and  the  uneaten  frag- 
ments of  the  roots  have  been  thrown  among  the  litter, 
the  spores  of  the  disease  have  been  found  to  live  un- 
harmed through  the  making  and  rotting  of  the  manure, 
so  that  fresh  land  may  thus  become  infected  when  the 
dung  is  carried  on  to  it.  Similarly,  when  hop  bines  are 
used  as  litter,  the  spores  of  the  hop  mildew  are  not 
destroyed  ;  but  no  other  cases  of  transmission  of  disease 
have  been  investigated.  As  regards  weeds,  farmyard 
manure  is  very  commonly  employed  for  root  crops,  in 
which  case  the  usual  cultivations  will  keep  down  any 
weeds  whose  seeds  are  in  the  dung,  and  when  the  dung 
is  put  on  grass  land  the  weed  seeds  stand  little  chance 
of  establishing  themselves. 

The  value  of  farmyard  manure  to  the  land  is  by 
no  means  confined  to  its  fertilising  action  ;  its  physical 
effects  upon  the  texture  and  water-holding  powers  of 
the  soil  are  equally  important ;  indeed,  for  some  crops, 
and  particularly  in  droughty  seasons,  these  factors 
count  for  more  than  fertilisers  towards  ensuring  a  good 
yield.  The  farmyard  manure,  as  it  rots  down  in  the 
soil,  goes  to  restore  the  stock  of  humus,  which  otherwise 


VII.]  PHYSICAL  EFFECTS  OF  MANURE  217 

is  always  tending  to  oxidise  and  diminish,  and  the 
humus,  considered  merely  from  the  physical  side, 
contributes  largely  to  the  fertility  of  the  soil.  In  the 
first  place,  it  improves  the  texture  of  all  soils ;  to  sands 
it  gives  cohesion  and  water-retaining  power,  while  by 
loosely  binding  together  the  finest  particles  of  clay  soils 
it  renders  them  more  porous  and  friable.  When  a  piece 
of  old  grass  land,  even  on  the  stiffest  of  soils,  has  been 
ploughed  up  it  is  easy  to  see  the  beneficial  effect  of 
the  humus  that  has  been  accumulated  ;  after  the  winter 
the  plough  slice  will  crumble  naturally  so  as  to  harrow 
down  at  once  to  a  mellow  seed-bed,  whereas  a  neigh- 
bouring piece  of  the  same  soil  that  has  long  been  under 
arable  cultivation  will  only  show  a  number  of  harsh 
intractable  clods.  The  importance  of  a  good  seed-bed 
to  the  future  well-being  and  ultimate  yield  of  the  crop 
can  hardly  be  exaggerated  ;  it  is  the  basis  of  all  good 
farming ;  so  that  even  when  the  fertilising  properties  of 
farmyard  manure  have  been  replaced  by  artificial 
manures,  some  other  means,  such  as  the  ploughing-in 
of  green  crops,  must  be  resorted  to  in  order  to  maintain 
the  stock  of  humus.  Of  course,  the  value  of  humus — 
and  in  this  respect  of  farmyard  manure — will  vary  on 
different  soils  and  with  different  crops ;  cereals,  for 
example,  are  comparatively  unaffected  by  its  absence, 
as  may  be  seen  by  the  manner  in  which  Mr  Prout 
grows  cereals  almost  continuously  on  his  strong  soil 
with  artificial  fertilisers  only,  but  root  crops  are  very 
dependent  on  a  mellow  seed-bed.  This  may  be  seen  on 
the  Rothamsted  plots ;  the  wheat  which  has  now  been 
grown  on  the  same  land  for  sixty-five  years,  comes  as 
well  and  yields  as  big  crops  on  the  plots  receiving  only 
artificial  manures  as  it  does  on  the  plot  receiving  dung, 
but  on  the  mangold  field  the  result  is  different.  Where 
artificial  manures  containing  no  organic  matter  have 


2i8  ^      FARMYARD  MANURE  [chap. 

been  supplied,  the  tilth  is  bad,  and  in  trying  seasons, 
when  drought  succeeds  heavy  rain  soon  after  sowing, 
the  plant  obtained  is  so  imperfect  as  to  reduce  the  yield 
considerably.  If  the  conditions  are  favourable  to 
germination  and  the  plant  once  becomes  established, 
then,  as  we  have  previously  seen  in  Table  LXVII.,  the 
plot  manured  with  minerals  and  nitrate  of  soda  will 
grow  a  bigger  crop  than  that  receiving  dung ;  but  this 
superiority  is  masked  in  many  seasons  by  the  defective 
plant  resulting  from  the  bad  texture  of  the  soil.  Table 
LXVII  I.  shows  the  proportion  the  number  of  roots  on 
each  plot  bears  to  the  possible  number,  as  calculated 

Table  LXVII  I.— Number  of  Mangold  Plants  as  Percentages  of 
THE  Possible.    Average  of  7  years,  1901-1907. 


Farmyard 
Manure,  etc. 

Mii:erals  and 
Nitrate  of  Soda. 

Minerals  and 
Rape  Cake. 

69 

62 

83 

from  the  width  of  the  rows  and  the  distance  apart  at 
which  they  are  singled,  for  three  plots,  one  of  which 
receives  farmyard  manure,  minerals  and  nitrate  of  soda, 
another  only  the  minerals  and  nitrate  of  soda,  and  the 
third,  minerals  and  rape  cake,  as  an  organic  source  of 
nitrogen. 

These  are  average  figures  for  a  period  which  includes 
several  years  when  a  very  good  plant  was  obtained  all 
over  the  field,  and  only  one  of  the  occasional  years 
when  the  plant  failed  entirely  on  the  plots  receiving  no 
organic  manure.  It  is  noticeable  that  the  plot  receiving 
rape  cake  (2000  lb.  every  year)  is  actually  better  as 
regards  the  number  of  plants  it  carries  than  the  dunged 
plot,  because  the  repeated  dressings  of  an  organic 
manure  like  rape  cake  supply  enough  humus  to  maintain 


VII.] 


PH  YSICAL  EFFECTS  OF  MANURE 


219 


the  texture  without  getting  the  soil  too  open — a  defect 
which  is  now  beginning  to  overtake  the  plot  that  has 
been  so  continuously  treated  with  large  amounts  of 
farmyard  manure. 

A  soil  which  has  been  enriched  in  humus  by 
repeated  applications  of  farmyard  manure  will  resist 
drought  better  than  one  in  which  the  humus  is  low ; 
the  difference  is  seen,  not  so  much  in  the  greater  amount 
of  moisture  present  in  the  soil  containing  humus,  as 
in   the  way  it   will  absorb   a   large  amount   of  water 

Table  LXIX. — Percentages  of  Water  in  Rothamsted  Soils. 


Depth. 

Broadbalk  Wheat. 

H008  Barley. 

Unmanured. 

Dunged. 

Unmanured. 

Dunged. 

Inches. 

0  to     9 

9  .,   18 
18  „  27 

i6'0 
19-8 
23.3 

19-3 
I7-0 
18-4 

I7-0 
22-5 
22-1 

20-7 

17-7 
18.3 

temporarily  during  heavy  rainfall  and  then  let  it  work 
more  slowly  down  into  the  soil,  thus  keeping  it  longer 
within  reach  of  the  crop.  Good  examples  are  afforded 
by  the  Rothamsted  plots ;  samples  of  soil  were  taken 
from  the  wheat  land  on  13th  September  1904;  on 
the  previous  day  0-262  inch  of  rain  had  fallen,  but 
for  nine  days  before  there  had  been  little  or  no  rain. 
The  portions  of  the  plots  from  which  the  samples  were 
drawn  had  been  fallowed  through  the  summer,  so  that 
the  drying  effect  of  the  crop  is  eliminated.  Samples 
were  also  taken  from  the  barley  plots  on  3rd  October 
of  the  same  year;  0-456  inch  of  rain  had  fallen  on  the 
30th  September,  before  which  there  had  been  fifteen 
days  of  fine  weather.  Table  LXIX.  shows  the  water 
in   the   soil   of  the  unmanured   and  the  continuously 


220  FARMYARD  MANURE  [chap. 

dunged  plots  respectively,  calculated  as  percentages  of 
the  fine  earth  from  which  the  stones  had  been  sifted. 

It  is  thus  seen  that  in  both  cases  the  dunged  soil, 
rich  in  humus,  had  retained  more  of  the  comparatively- 
recent  rainfall  near  the  surface,  so  that  the  top  soil  was 
moister,  while  the  subsoil  was  drier.  The  difference  in 
favour  of  the  surface  soil  is  about  3-  5  per  cent,  which 
on  that  soil  would  amount  to  about  30  tons  per  acre,  or 
approximately  0-3  inch  of  rain.  It  is  thus  seen  that 
the  surface  soil  of  the  dunged  plot  had  retained 
practically  the  whole  of  the  preceding  rainfall :  and  the 
greater  dryness  of  the  subsoil  is  due  to  the  way  the 
soil  has  kept  back  the  small  rainfalls,  which  have 
evaporated  instead  of  being  passed  on  to  the  subsoil,  as 
happens  on  the  unmanured  plots.  The  same  fact  is 
illustrated  by  the  behaviour  of  the  drains,  which  lie 
below  the  centre  of  each  of  the  wheat  plots  at  a  depth 
of  30  inches ;  below  the  dunged  plot  the  drain  very 
rarely  runs — only  after  an  exceptionally  heavy  and 
long-continued  fall ;  whereas  the  drain  below  the 
unmanured  plot  runs  two  or  three  times  every  winter. 
Putting  aside  the  greater  drying  effect  of  the  much 
larger  crop  on  the  dunged  plot,  the  difference  is  mainly 
due  to  the  way  the  surface  soil  rich  in  humus  absorbs 
more  of  the  water  at  first,  and  then  lets  the  excess 
percolate  so  much  more  slowly  that  the  descending 
layer  of  over-saturation,  which  causes  the  drain  to  run, 
rarely  or  never  forms. 

The  water-retaining  power  of  the  dung  may  also  be 
seen  in  the  superior  yield  of  the  dunged  plots  in 
markedly  dry  seasons.  Table  LXX.  shows  a  com- 
parison of  the  yield  on  Plot  2,  receiving  14  tons  of 
dung,  and  Plot  7,  receiving  a  complete  artificial  manure, 
for  the  years  1879,  which  was  exceptionally  wet  and 
cold,  and  for  1893,  which  was  hot  and  dry  throughout 


VII.J 


PHYSICAL  EFFECTS  OF  MANURE 


221 


the  growing  period  of  the  plant.  The  rainfall  for 
this  period,  ?>.,  for  the  four  months  March  to  June, 
was  13  inches  in  1879  and  only  2-9  inches  in  1893. 
The  average  yield  on  the  dunged  plot  is  about 
3  bushels  more  than  on  Plot  7,  but  in  the  dry  year  its 
superiority  amounted  to  14  bushels,  whereas  in  the  very 

Table  LXX.— Effect  of  Farmyard  Manure  in  Dry  and  Wet 
Seasons.    Wheat.    (Rothamsted.) 


Plot. 

1879 
(Wet). 

1S93 
(Dry). 

Average, 
51  years. 

2 

7 

Bushels. 
16-0 
16-25 

Bushels. 

34-25 
20-25 

Bushels. 

35-7 
32-9 

wet  year  the  two  plots  sank  to  the  same  low  level.  In  a 
bad  season  the  bacterial  changes,  which  render  the  plant 
food  in  dung  available  for  the  crop,  go  on  very  slowly. 

It  has  been  suggested  that  farmyard  manure  may 
have  an  effect  upon  the  water-content  of  the  soil  by 
reducing  the  surface  tension  of  water  with  which 
it  comes  in  contact.  If  the  surface  tension  of  the 
soil  water  were  thus  reduced,  it  would  be  less  readily 
lifted  to  the  surface  and  therefore  less  available  to 
shallow-rooted  plants,  but  more  conserved  in  the  lower 
layers  of  the  soil.  Although  an  extract  of  dung 
possesses  a  lower  surface  tension  than  pure  water,  the 
facts  concerning  its  behaviour  in  the  soil  are  very 
obscure  as  yet,  and  the  figures  just  quoted  as  to  the 
relative  distribution  of  moisture  under  dunged  and 
unmanured  plots  lend  no  support  to  the  theory. 

The  application  of  farmyard  manure  to  grass  land, 
not  only  has  a  fertilising  and  water-retaining  effect,  but 
is  also  valuable  from  the  way  it  acts  as  a  mulch  and 
affords  the  springing  grass  in  the  early  months  of  the 


22i  FARMYARD  MANURE  [chap. 

year  some  protection  from  cold  and  drying  winds.  At 
Rothamsted  on  the  permanent  grass  plots  it  is  often 
noticed  that  the  plots  which  receive  applications  of 
farmyard  manure  once  in  every  four  years  start  a  little 
earlier  and  make  a  quicker  growth  than  the  others. 
This  mulching  effect  partly  accounts. for  the  great  value 
attached  to  dung  as  a  dressing  for  permanent  grass 
land  on  open  chalky  soils,  as  in  Wiltshire,  where 
it  is  customary  to  reserve  all  the  farmyard  manure 
for  the  grass  and  farm  the  arable  land  entirely  with 
artificial  manures,  aided  by  the  folding  off  of  catch 
crops.  Such  a  practice  is  wasteful  of  the  farmyard 
manure  as  a  fertiliser,  for  the  loss  of  nitrogen  from 
a  layer  spread  loosely  over  the  ground  until  it  decays  is 
considerable,  but  the  waste  is  tolerated  in  view  of  the 
gain  to  the  physical  or  mechanical  condition  of  the 
land. 

In  ordinary  mixed  farming  undoubtedly  the  best 
way  of  utilising  farmyard  manure  is  to  apply  it  to  the 
root  crops,  and  especially  to  mangolds  and  potatoes. 
Swedes  require  much  less  nitrogen  than  do  the  other 
root  crops.  They  also  require  a  firm  but  fine  tilth ;  in 
consequence,  not  more  than  lo  to  12  tons  of  dung 
per  acre  should  be  given  for  Swedes  and  it  should  be 
applied  in  the  autumn,  in  order  that  it  may  become 
well  rotted  down  before  the  spring  cultivation  begins. 
But  up  to  20  tons  of  dung  per  acre  can  be  profitably 
employed  for  mangolds  and  potatoes,  and  it  can  if 
necessary  be  applied  immediately  before  sowing.  Any 
surplus  dung,  after  the  requirements  of  the  root  crops 
have  been  satisfied,  is  probably  best  given  to  the  young 
seeds  in  the  early  winter,  to  act  both  as  a  fertiliser 
and  as  a  mulch.  The  seeds  benefit  greatly,  and  at  the 
same  time  much  of  the  added  fertility  is  retained  for 
the  corn  crop  that  follows ;  manuring  the  young  seeds 


VII.]  COST  OF  FARMYARD  MANURE  223 

is  certainly  preferable  to  the  very  general  custom  of 
manuring  the  old  ley  before  it  is  ploughed  up  for  wheat 
or  oats.  A  certain  amount  of  the  farmyard  manure 
made  on  the  farm  should,  however,  always  be  reserved 
for  the  meadow  land,  especially  on  light  soils  and  on 
land  comparatively  newly  laid  down  to  grass.  Of 
course  dung  would  be  wasted  on  rich  grazing  land  ;  it 
is  the  thin  light  soils  that  are  cut  for  hay,  or  grass  land 
that  has  only  been  laid  down  for  a  few  years  and 
has  had  no  time  to  accumulate  a  stock  of  humus, 
which  are  most  benefited  by  an  occasional  dressing 
of  farmyard  manure — once  in  every  four  or  five 
years. 

What  price  should  be  set!  upon  a  ton  of  farmyard 
manure  is  a  question  often  asked,  but  no  general  answer 
is  possible,  so  much  depends  upon  the  other  conditions 
prevailing  upon  the  farm.  As  a  rule,  farmyard  manure 
is  part  of  the  normal  output  of  the  farm  ;  the  farmer  has 
only  to  make  it  and  use  it  to  the  best  advantage,  he 
is  not  concerned  with  the  question  of  whether  it  would 
be  cheaper  to  replace  it  with  an  equivalent  amount  of 
some  other  fertiliser.  There  are,  however,  occasions 
when  the  problem  does  arise  of  whether  it  is  cheaper 
to  make  farmyard  manure,  to  buy  it,  or  to  attempt 
to  replace  it  by  artificials ;  for  example,  the  men  who 
are  farming  specially  for  potatoes  or  hops  often  fatten 
bullocks  or  pigs  solely  for  the  sake  of  the  manure  thus 
made,  and  are  content  to  lose  money  on  the  live  stock 
because  of  the  value  of  the  dung.  Since  farmyard 
manure  made  in  this  way  is  often  a  very  expensive 
Particle,  it  is  important  to  try  and  put  some  monetary 
value  on  it,  so  that  the  farmer  may  attain  a  clearer  idea 
of  the  profit  or  loss  attached  to  the  keeping  of  live 
stock  as  manure  makers.  It  is,  of  course,  possible  to 
treat   farmyard    manure   like   any  other   fertiliser   and 


224                           FARMYARD  MANURE  [chap. 

value  it  on  the  unit  system  (see  p.  348),  the  result  of 
which  would  be  somewhat  as  follows  : — 
Farmyard  manure  contains — 

0'6  per  cent.  Nitrogen  at  12s.   .             ,=  £072, 

0-3  per  cent.  Phosphoric  Acid  at  3s.     .   =  o    oil 

0-5  per  cent.  Potash  at  4s.         .            .   =  020 

Value  per  ton  .   =  ;^o  10     i 


Much  weight  cannot,  however,  be  attached  to  such  a 
valuation,  because  the  unit  values  are  taken  from  con- 
centrated manures  and  do  not  apply  to  dung ;  for 
example,  nitrogen  in  waste  materials  like  shoddy  can 
often  be  obtained  at  half  the  price  paid  for  it  in 
sulphate  of  ammonia  or  nitrate  of  soda,  and  considering 
the  slow  availability  of  much  of  the  nitrogen  in  dung  its 
unit  value  should  be  much  below  12s.  On  the  other  hand, 
the  organic  matter  supplied  in  the  farmyard  manure  is 
not  valued  ;  yet  it  is  for  the  effect  of  this  organic  matter 
on  the  texture  of  the  soil  that  farmyard  manure  is  most 
generally  required.  The  cost  of  handling  farmyard 
manure,  which  is  so  much  greater  than  it  is  for  an 
equivalent  amount  of  artificial  fertiliser,  should  also  be 
taken  into  comparison  but  cannot  well  be  estimated, 
because  it  will  vary  on  each  farm. 

While  it  is  thus  practically  impossible  to  value  farm- 
yard manure  on  its  composition,  a  proper  system  of 
book-keeping  will  show  what  it  costs  to  make,  in  a 
manner  that  is  independent  of  the  profit  and  loss 
upon  the  live  stock.  In  this  way  a  farmer  can  form 
for  himself  a  clear  idea  of  the  economics  of  dung-making 
as  compared  with  the  purchase  of  either  town  manure  or 
artificial  fertilisers.  The  most  valid  principle  on  which 
a  cost  can  be  worked  out,  and  one  which  does  justice 
equally  to   the   live  stock   and   to   the    manure,   is    to 


VII.]  COST  OF  FARMYARD  MANURE  42$ 

charge  the  dung  with  the  cost  of  the  Htter  and  with 
the  manure  value  of  all  the  foods  consumed  in  the 
yards  or  boxes.  These  manure  values  are  what  the 
valuer  would  allow  to  an  outgoing  tenant  for  the 
fertilising  material  which  he  brought  on  to  the  farm 
during  the  last  year  of  his  tenancy  and  which  he  leaves 
behind  in  the  form  of  dung.  Of  course  the  valuer 
does  not  allow  compensation  for  the  roots,  hay,  and 
straw  grown  on  the  farm ;  these,  however,  must  be 
reckoned  in  making  up  the  cost  of  the  dung. 

The  manure  value  of  any  food  (see  p.  356)  is  based 
upon  its  composition  and  represents  the  value  at  current 
market  rates  of  whatever  part  of  the  food  has  a  fertilis- 
ing value  and  may  be  supposed  to  find  its  way  into  the 
manure ;  the  values  employed  below  are  those  recom- 
mended by  the  Central  Chamber  of  Agriculture  for 
adoption  in  farm  valuations  and  have  been  obtained  by 
the  method  to  be  shortly  described.  To  arrive  at  the 
cost  of  the  dung  the  manure  values  of  all  the  food  con- 
sumed must  be  taken  and  added  to  the  whole  cost  of 
the  litter,  whether  straw  or  peat  moss ;  the  sum  is  then 
divided  by  the  amount  of  manure  ascertained  to  have 
been  made.  In  Table  LXXI.  this  principle  is  applied  to 
the  data  obtained  from  some  of  the  feeding  experiments 
already  quoted  (pp.  196-9),  and  also  to  two  cases  extracted 
from  the  accounts  of  an  ordinary  farm.  The  first 
column  gives  the  nature  of  the  food  and  the  second  its 
manure  value  per  ton  ;  the  remaining  double  columns 
give  for  each  food  the  amount  consumed  in  the  experi- 
ment and  its  manure  value.  The  cost  of  the  litter  is 
set  out  below,  and,  added  to  the  manure  values,  gives 
the  total  cost  of  the  manure  made  in  each  case,  the 
amount  of  which  is  also  shown.  Working  on  these 
lines  we  learn  that  farmyard  manure  costs  from  5s.  to 
I2S.  a  ton  to  make  on   the   farm,  without  taking  into 

P 


226 


FARMYARD  MANURE 


[chap. 


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Quantity  dung  made 
Cost  oer  ton 

Foods. 

Peas 

Mangolds 
Swedes     . 
Decorticated 

li 

cotton  cake    . 
Linseed  cake    . 
Oats 

Barley     . 
Maize  meal       , 
Bran 
Straw 
Hay 
Litter  :— 

&  • 

in  0 

<D     4-> 

Vii.l  COST  OF  FARMYARD  MANURE  227 

account  any  profit  or  loss  on  the  live  stock,  because 
this  latter  question  is  so  much  dependent  upon  the  turn 
of  the  market  and  the  skill  of  the  dealer.  It  is  neces- 
sary to  discriminate  and  to  keep  distinct  the  two 
operations — the  making  of  dung  and  the  fattening  of 
the  cattle — so  that  a  conclusion  can  be  reached  as  to  the 
profitableness  of  each  separately.  Of  course  in  making 
out  the  charges  against  the  cattle,  the  whole  cost  of 
the  cake,  etc,  which  they  consume  must  not  be  put  down, 
but  only  that  part  of  it  which  is  not  debited  to  the  dung 
as  manure  value ;  e.g.,  if  a  ton  of  linseed  cake  cost  £^^ 
only  £6,  2s.  should  be  charged  against  the  stock  for 
food,  because  £i,  i8s.,  its  manure  value,  would  be 
charged  to  the  manure. 

To  make  this  clearer,  we  can  draw  up  a  balance- 
sheet  for  the  feeding  of  two  of  the  heifers  already 
mentioned  : — 

Table  LXXfl.— Cambridge,  No.  2. 

Dr. 

Purchase  price  of  2  Heifers  30    o 

6  tons  of  Mangolds  at  5s.   . 

\  ton  of  Hay  at  45s. 

6    cwts.    of    Decorticated 

Cotton  Cake  at  £^ 
Attendance,  12    weeks    at 

6d 

Balance,  being  profit 

Total 


£      S.     D. 

Cr.                                          &    s. 

D. 

30  0  0 

Manurevalue  of  Mangolds     015 

0 

I  10    0 

I      2     6 

11              Hay          .     0    7 
„              Cake        .     0  16 

6 
10 

280 

(Charged  to  Dung) 
Sale  price  of  Heifers          .  34    0 

0 

060 

0  12   10 

35  19    4 

Total        .        .  35  19 

4 

Thus  the  feeding  has  resulted  in  a  small  profit  of 
1 2s.  lod.,  and  at  the  same  time,  as  was  shown  in  Table 
LXXI.,  5  J  tons  of  farmyard  manure  were  made  at  a  cost 
of  I  IS.  8d.  per  ton,  or  if  the  heifers  are  considered  to  have 
been  fattened  solely  for  the  purposes  of  making  dung 
and  the  two  accounts  are  combined  by  crediting  the 
I2S.  lod.  profit  to  the  dung,  the  latter  has  cost  about 
9s.  4d.  per  ton, 


228  FARMYARD  MANURE  [chap.  vii. 

This  figure,  about  los.  per  ton  for  farmyard  manure, 
is  considerably  higher  than  the  usual  estimate  attached 
to  dung  for  purposes  of  valuation  or  of  drawing  up  the 
the  balance-sheet  of  a  manurial  experiment ;  it  does, 
however,  represent  what  it  will  cost  the  potato  or  hop 
grower  who  sets  out  to  keep  cattle  solely  for  the  purpose 
of  making  dung.  It  is  for  him  to  decide  whether  he  can 
secure  sufficient  profit  from  the  cattle  themselves  to 
make  it  worth  while  to  buy  farmyard  manure  at  such 
a  price.  A  big  cake  bill  is  indeed  a  great  source  of  loss 
on  many  farms ;  unless  the  cattle  themselves  pay  for 
their  food,  the  increased  richness  of  the  dung  due  to  the 
purchased  food  will  not  produce  a  very  remunerative 
increase  in  the  crops. 


CHAPTER  VIII 

PERUVIAN    GUANO    AND    OTHER    MIXED 
FERTILISERS 

Origin  of  the  Deposits  of  Guano — Variation  in  Composition  with 
Age — Compounds  of  Nitrogen  present  in  Peruvian  Guano 
— Ichaboe  and  Damaraland  Guanos — Fish  Guano — Meat 
Guano — Dried  Blood — Greaves — Rape  Dust  and  other  Cake 
Residues— Manures  derived  from  Faecal  Matter— Sewage 
Sludges. 

The  term  "guano"  (Spanish  kuano  =  dung)  is  properly 
restricted  to  a  fertilising  material  consisting  almost 
wholly  of  the  excreta  of  sea  birds,  which  has  accumu- 
lated upon  certain  oceanic  islands  where  rain  rarely 
falls.  The  original  guano  came  from  islands  off  the 
coast  of  Peru  between  the  7th  and  20th  degrees  of 
south  latitude,  and  this  "Peruvian  Guano"  still  forms 
the  bulk  of  our  importations,  although  since  the  time 
of  the  first  introduction  of  guano,  other  deposits,  formed 
under  similar  conditions  of  climate  and  situation,  have 
been  opened  up.  All  these  deposits,  being  of  similar 
origin,  possess  many  features  in  common.  The  islands, 
small  and  uninhabited,  are  the  resort  for  breeding 
purposes  of  enormous  ilocks  of  pelicans,  albatrosses,  and 
other  oceanic  birds,  which  resort  to  land  only  in  their 
breeding  season.  On  the  favoured  spots  they  nest  very 
closely,  and  the  young  birds  after  they  are  hatched  are 
fed  for  a  month  or  more  with  great  quantities  of  fish 

2^9 


230 


PERUVIAN  GUANO,  ETC. 


[chap 


brought  by  the  parent  birds.  In  addition  to  the  excreta 
the  deposit  will  thus  also  contain  many  carcases  of 
young  birds  dying  from  some  cause  or  other,  fragments 
of  fish,  feathers,  seaweed,  and  even  sand  and  stones 
originally  swallowed  by  the  parent  birds.  When  the 
birds  leave  the  island  the  tropical  sun  and  the  intense 
dryness  of  the  atmosphere  rapidly  desiccate  the 
accumulated  materials  and  prevent  any  change  or  loss 
by  fermentation. 

The  excreta  of  the  birds,  which  is  the  starting-point, 
is  highly  nitrogenous,  consisting  very  largely  of  uric 
acid,  together  with  a  fair  amount  of  phosphoric  acid 
derived  from  the  fish,  which  is  the  exclusive  diet  of  the 
birds.  An  old  analysis  of  a  white  Peruvian  deposit, 
consisting  mainly  of  recently  deposited  excreta,  showed 
as  much  as  18-3  per  cent,  of  nitrogen  and  only  9-2  per 
cent,  of  phosphoric  acid. 

Table  LXXIII. — Analysis  of  Freshly-deposited  Guano. 


Water 

Organic  Matter  and  Ammonium  Salts 
Containing  Nitrogen     . 
Phosphoric  Acid   .... 

Lime    .         .         .... 

Alkaline  Salts       .... 

Sand 

10-9 
65-63 
(18-32) 
9-20 
6 -08 
6-43 
1.76 

Dry  as  is  the  climate  a  certain  amount  of  change 
still  goes  on ;  the  uric  acid  is  fermented  to  urea  and  to 
ammonium  salts,  some  of  which  are  volatilised,  while 
the  occasional  rains  dissolve  out  both  the  ammonium 
compounds  and  soluble  phosphates  and  the  alkalis.  As 
a  result,  the  composition  of  guano  deposits  is  extremely 
variable,  both  in  the  different  strata  of  one  deposit 
and  still  more  in  passing  from  island  to  island.  The 
older  a  deposit  is,  and  the  greater  the  washing  it  has 


VIII.]  IMPORTATIONS  OF  GUANO  231 

received,  the  more  will  it  have  lost  nitrogen  and  the 
richer  will  it  have  grown  in  phosphoric  acid,  until  from 
the  material  described  above  deposits  are  formed  con- 
taining little  or  nothing  beyond  phosphate  of  lime. 

The  analyses  (Table  LXXVII.)  will  show  how  great 
is  the  range  in  quality  that  thus  results. 

Peruvian  Guano. — Peruvian  guano  is  derived  from 
three  groups  of  islands  off  the  coast  of  Peru,  of  which 
the  most  important,  Chinchas,  is  a  little  south  of  Callao. 
The  fertilising  value  of  the  deposit  was  known  long 
prior  to  the  Spanish  occupation  of  the  country,  in  many 
parts  of  which  crops  could  only  be  obtained  by  the  aid 
of  guano. 

A.  von  Humboldt  was  the  first  European  to  call 
attention  to  the  use  of  guano ;  he  brought  samples 
home  with  him  about  1804,  at  which  time  he  found 
some  fifty  vessels  annually  employed  in  carrying  guano 
from  the  Chinchas  Islands  for  use  in  Peru. 

The  exportation  to  Europe,  however,  did  not  begin 
until  nearly  forty  years  later,  the  first  crops  being  landed 
in  Liverpool  early  in  1840.  The  success  of  the  manure 
was  rapid  and  the  exportation  soon  assumed  consider- 
able dimensions,  as  much  as  283,300  tons  reaching  the 
United  Kingdom  in  1845.  For  some  time  the  annual 
consumption  remained  at  a  very  high  figure,  but 
financial  troubles,  the  war  between  Peru  and  Chili,  the 
exhaustion  of  the  richest  deposits,  and  difficulties 
induced  by  adulteration  and  the  natural  variation  in  the 
composition  of  the  cargoes,  led  to  a  slackening  in  the 
demand.  During  the  last  few  years  the  exportation 
has  been  at  the  rate  of  about  60,000  to  70,000  tons  per 
annum,  of  which  the  United  Kingdom  consumed  about 
one-half. 

During  the  earlier  years  Peruvian  guano  was  derived 
from  the  Chinchas  Islands  only,  and  was  an  exceedingly 


232  PERUVIAN  GUANO,  ETC.  [chap. 

rich  deposit,  containing  1 1  to  15  per  cent,  of  nitrogen ; 
but  as  that  deposit  became  exhausted,  the  other  islands 
producing  a  poorer  material  were  in  turn  drawn  upon. 
Of  recent  years  it  has  been  found  that  new  deposits  have 
accumulated  on  the  Chinchas  Islands  to  such  an  extent  as 
to  justify  fresh  workings,  and  accordingly  a  guano  with 
a  very  high  percentage  of  nitrogen  is  again  obtainable. 
Another  of  the  islands,  Ballestas,  has  latterly  been 
yielding  a  very  rich  guano  with  more  than  12  per 
cent,  of  nitrogen  and  about  an  equal  amount  of 
phosphoric  acid,  and  now  it  is  expected  that  material 
of  this  class  will  always  be  available. 

It  is  difficult  to  form  an  adequate  idea  of  the 
enormous  bird  population  of  these  islands  and  the 
amount  of  food  consumed  during  the  breeding  season,  but 
a  recent  commission  which  visited  the  islands  estimated 
the  current  production  of  fresh  guano  as  10,000  tons  per 
annum.  Thus,  freshly  deposited  guano  is  light  grey  in 
colour  and  contains  about  16  per  cent,  of  nitrogen,  with 
9  of  phosphoric  acid,  the  usual  brown  colour  coming  as 
the  material  ages  and  undergoes  some  decomposition. 
A  law  has  been  recently  passed  ensuring  a  four- 
months  close  season  during  the  breeding  of  the  birds, 
and  the  Peruvian  Government  have  recently  forbidden 
the  working  of  the  deposits  during  this  close  season  in 
order  to  ensure  as  little  disturbance  as  possible.  The 
guano  islands  are  now,  in  fact,  being  regularly  "  farmed," 
and  the  exportations  will  consist  of  the  previous  years' 
rich  deposit,  together  with  a  certain  amount  of  the  older 
accumulated  stock. 

The  bulk  of  the  imports,  however,  consists  of 
material  containing  from  5  to  8  per  cent,  of  nitrogen, 
and  each  consignment  is  sold  on  the  basis  of  an  analysis 
of  a  sample  drawn  by  the  officials  of  the  Dock  Company 
as  the  vessel  unloads.     Another  class  of  material  has 


VIII.]        COMPOSITION  OF  PERUVIAN  GUANO 


233 


latterly  been  exported  in  large  quantities  ;  it  consists 
of  the  phosphatic  guanos  derived  from  the  Lobos 
Islands,  containing  as  much  as  60  per  cent,  of  calcium 
phosphate  and  only  from  2  to  3  per  cent,  of  nitrogen. 
In  addition  to  these  cargoes  of  varying  composition 
which  are  sold  in  the  condition  in  which  they  arrive, 
the  importers  make  up  a  mixture  to  a  standard  com- 
position with  about  7  per  cent,  of  nitrogen,  which  is 
sold  as  equalised  Peruvian  guano. 

Peruvian  guano,  as  imported,  is  a  loose  dry  powder, 
grey  in  the  richer  samples  and  becoming  browner  as  it 
grows  more  phosphatic.  As  a  rule,  it  is  friable  and 
may  be  sown  by  any  manure  distributor,  but  there 
are  found  in  it  occasional  fragments  of  slaty  rock, 
with  a  number  of  half-decayed  feathers  in  the  richer 
specimens.  It  possesses  a  strong  and  characteristically 
ammoniacal  smell  and  an  alkaline  reaction  due  to  the 
presence  of  ammonium  carbonate. 

The   following    detailed    analysis,   Table   LXXIV., 


Table  LXXIV.— Analysis  of  Chinchas  Guano, 

1897. 

Nitrogen  as  Nitrate 

0-32 

„         as  Ammonium  Salts          ,        . 

3-94 

„          as  Uric  Acid 

8-85 

„          in  other  Organic  Forms  .        t 

2-98 

Total  Nitrogen 

16.09 

Phosphoric  Acid  soluble  in  Water  . 

2-63 

„               soluble  in  Ammonium  Citrate 

6-29 

„                insoluble                  „ 

•37 

Total  Phosphoric  Acid,  all  soluble  in  I  per  cent. 

Citric  Acid  solution 

9-29 

equivalent  to  Tri-calcium  Phosphate    . 

20-28 

shows  the  composition  of  a  sample  of  the  Chinchas 
deposit ;  it  will  be  seen  that  the  nitrogen  is  mainly 
present  in  compounds  soluble  in  water — uric  acid,  a 
little  urea,  guanine,  and  ammonium  salts,  with  a  trace 
of  nitric   acid.      The  phosphoric  acid   is   also   largely 


234  PERUVIAN  GUANO,  ETC.  [chap. 

soluble  in  water,  being  combined  with  the  ammonia 
and  the  potash  and  soda  also  present  in  small 
quantities. 

Similar  detailed  analyses  are  not  available  for 
poorer  grades,  but  it  may  be  taken  as  a  general 
rule  that  the  lower  the  percentage  of  nitrogen,  the 
less  of  it  will  be  found  in  a  soluble  form,  and  the 
more  insoluble  will  the  phosphoric  acid  compounds 
have  become,  so  that  the  richest  guanos  are  also 
the  most  readily  available  for  the  plant.  It  is  also 
characteristic  of  a  good  guano,  and  to  this  much  of  its 
value  as  a  choice  fertiliser  is  due,  that  the  compounds 
of  nitrogen  present  are  very  varied  and  require  differ- 
ent series  of  bacterial  changes  in  the  soil  before  they 
become  available,  so  that  the  crop  is  fed  steadily  and 
continuously. 

It  is  this  property  and  the  fact  that  guano  is  naturally 
a  well-balanced  manure,  rich  in  phosphates  as  well  as 
nitrogen,  and  containing  also  a  small  proportion  of 
potash,  which  makes  guano  so  popular.  It  is  essentially 
a  safe  manure,  applicable  to  all  crops,  and  not  requiring 
the  skill  in  its  adjustment  to  the  land  or  the  crop  which 
is  necessary  with  the  more  active  single  manures  like 
nitrate  of  soda,  etc.  Again,  coming  into  action  con- 
tinuously and  equably,  it  is  more  calculated  to  yield 
produce  of  high  quality  than  more  concentrated 
manures ;  it  is  therefore  specially  suited  for  fruit  and 
similar  valuable  crops.  As  a  natural  consequence  of 
these  advantages  the  good  Peruvian  guanos  are  always 
somewhat  dearer  than  other  manures  when  valued  on 
a  unit  basis,  the  extra  price  representing  partly  the 
value  of  this  natural  blending  and  partly  the  long 
farming  tradition  of  the  excellence  of  guano,  which  was 
the  earliest  of  the  concentrated  manures  to  find  a  large 
sale  in  this  country. 


VIII.]  ADULTERATIONS  OF  GUANO  235 

Few  fertilisers  have  been  subjected  to  a  greater 
amount  of  sophistication  and  adulteration  than  has 
Peruvian  guano,  but  since  the  passing  of  the  Fertilisers 
and  Feeding  Stuffs  Act,  and  the  better  organisation 
of  its  sale  from  a  single  distributing  centre,  there 
has  been  but  little  fraud.  It  should  always  be  found 
on  receipt  to  be  in  the  sealed  bags  of  i^-  cwt.  in  which 
it  is  distributed,  and,  as  with  all  manures  of  variable 
composition,  the  guarantee  should  be  checked  by 
analysis,  so  as  to  ensure  the  delivery  has  been  made 
from  the  specified  cargo.  Deliberate  adulterations  with 
sand  or  dirt  can  generally  be  detected  by  the  incinera- 
tion of  a  sample,  the  incombustible  residue  should  be 
white,  and  show  but  few  signs  of  red  oxide  of  iron. 

A  certain  arnount  of  Peruvian  guano  is  treated  with 
sulphuric  acid,  so  as  to  convert  the  ammonium  carbonate 
into  non-volatile  ammonium  sulphate,  and  also  to  render 
a  larger  proportion  of  the  phosphoric  acid  soluble.  In 
this  way  is  obtained  "  dissolved  Peruvian  guano,"  which 
is  made  to  contain  about  6  per  cent  of  nitrogen  and  10 
per  cent,  of  phosphoric  acid,  of  which  9  per  cent,  is 
soluble  in  water.  The  use  of  acid  adds  to  the  value 
of  the  guano,  and  not  only  will  it  store  and  travel 
with  less  risk  of  deterioration  through  volatilisation  of 
ammonium  carbonate,  but  the  increased  solubility  of  the 
phosphates  present,  and  their  consequent  activity,  makes 
the  whole  a  better  balanced  manure. 

Compared  with  the  Peruvian,  the  other  deposits  of 
guano  which  can  be  classed  as  nitrogenous  are  com- 
paratively unimportant,  and  only  those  from  Ichaboe 
Island  and  Damaraland  on  the  south-west  coast  of 
Africa  have  of  late  been  articles  of  commerce  in  this 
country. 

The  Damaraland  deposits  are  apparently  exhausted, 
while   shipments   of   Ichaboe   guano   only  come   inter- 


236  PERUVIAN  GUANO,  ETC.  [chap. 

mittently,   when    the    requirements    of    Cape    Colony 
have  been  satisfied. 

Ichaboe  guano  only  represents  the  deposit  of  a 
single  year,  it  is  thus  very  fresh  and  distinguished  by 
the  undecomposed  feathers  it  contains.  With  about  8 
per  cent,  of  nitrogen,  it  is  usually  proportionally  less 
rich  in  phosphoric  acid  than  a  similar  grade  of  Peruvian 
guano  would  be.     It  usually  also  contains  more  sand. 

On  the  many  other  oceanic  islands  where  guano  has 
been  deposited,  the  occasional  rains  or  heavy  dews  have 
been  sufficient  to  remove  the  soluble  nitrogen  com- 
pounds and  even  in  time  the  organic  nitrogen  bodies, 
which  in  the  presence  of  moisture  have  been  able  to 
decay  and  break  down  into  soluble  material,  leaving 
behind  a  residue  consisting  mainly  of  phosphate  of 
lime.  In  other  cases  chemical  reactions  have  taken 
place  with  the  calcium  carbonate  of  the  coral  rock  on 
which  the  deposit  happened  to  be  formed,  resulting  in 
the  production  of  a  calcium  phosphate,  containing  some- 
times rather  a  large  proportion  of  iron  and  alumina. 
These  phosphates,  at  one  time  of  importance  in  the 
manufacture  of  superphosphates,  will  be  dealt  with 
under  phosphatic  manures. 

Besides  the  true  guanos  derived  from  bird  drop- 
pings and  the  closely  allied  bat  guanos,  small  deposits 
of  which  are  found  in  caves  in  America  and  South 
Africa  but  which  possess  no  commercial  importance,  a 
good  many  other  substances  containing  nitrogen  and 
phosphoric  acid  are  called  guano,  though  they  have  no 
proper  claim  to  the  title.  For  example,  the  residues 
from  various  processes  dealing  with  fish  {e.g.,  in  the 
preparation  of  cod  liver  oil,  the  curing  of  herrings,  the 
tinning  of  sardines,  etc.),  are  dried  and  reduced  to  a 
powder,  which  is  sold  as  "  fish  guano  "  ;  and  again,  meat 
residues,  such  as  accumulate  in  the  manufacture  of  meat 


VIII.]  PISH  GUANO  111 

extracts,  are  similarly  dried  and  disintegrated  for  sale 
as  "  meat  guano " ;  even  some  forms  of  dried  sewage 
sludge  masquerade  under  the  name  of  guano. 

Fish  guano  is  manufactured  in  many  places  where 
any  considerable  fish  waste  is  available.  The  oil  is 
extracted  by  heat  and  pressure,  and  the  remaining 
material  is  dried  and  disintegrated  as  finely  as  possible. 
Considering  the  very  varied  origin  of  fish  guano,  its 
composition  is  remarkably  constant :  the  nitrogen 
varies  between  6  and  9  per  cent,  the  phosphoric  acid 
represents  from  13  to  20  per  cent,  of  tri-calcic  phos- 
phate. The  fineness  of  grinding  is  less  uniform ;  two 
classes  of  fish  guano  are  found  :  in  one  of  them  the 
material  is  reduced  to  a  light  fluffy  powder,  the  other 
is  denser  and  contains  pieces  of  hard  bone  up  to  a 
quarter  of  an  inch  in  diameter.  This  coarsely  ground 
material  must  be  less  available,  at  any  rate  as  regards 
the  phosphates.  Fish  guanos  generally  contain  a 
distinct  amount  of  oil  which  has  not  been  removed 
in  the  manufacture ;  it  has  been  suggested  that  more 
than  3  per  cent,  should  be  regarded  as  detrimental 
to  the  value,  but  this  opinion — that  the  presence  of  oil 
delays  the  decomposition  of  such  manures — has  really 
never  been  demonstrated. 

Fish  guano  is  a  comparatively  active  nitrogenous 
manure,  since  some  of  the  compounds  it  contains  are 
soluble  in  water  and  are  rapidly  decomposed  by  bac- 
teria ;  the  main  constituents  are,  however,  proteins  and 
gelatinoids  which  resist  attack  to  a  greater  or  less 
degree.  In  consequence  fish  guano  shares  with  the 
true  guanos  the  property  of  continuing  to  yield 
nitrogen  available  to  the  plant  throughout  the  whole 
growing  season,  though  the  range  of  compounds  in  fish 
guano  must  be  regarded  as  a  little  less  active  than 
those  in  Peruvian   guano.     Fish  guano  has  for  many 


238  PERUVIAN  GUANO,  ETC.  [chap. 

years  been  a  favourite  manure  among  hop  growers ; 
it  is  also  occasionally  used  for  root  crops  when  farm- 
yard manure  is  not  available.  It  should  be  applied 
early  in  the  year,  when  the  land  is  first  worked,  and 
it  should  be  dug  or  ploughed  into  the  land  as  soon  as 
sown,  otherwise  rooks  and  other  birds  will  eat  it  as 
long  as  they  are  allowed  to  do  so.  Like  all  manures 
of  this  class,  it  is  injurious  to  germinating  seeds  or  the 
tender  rootlets  of  growing  plants,  until  it  has  been  in 
the  soil  for  a  short  time  and  the  first  active  fermenta- 
tion is  over. 

Meat  guano  is  prepared  from  all  kinds  of  slaughter- 
house refuse  in  much  the  same  way  as  fish  guano — the 
waste  of  carcases,  condemned  imported  meat,  tallow 
boilers  refuse,  the  residues  obtained  in  making  meat 
extracts,  and  so  forth,  are  heated  and  pressed  to 
remove  fat,  and  the  residue  is  then  finely  ground. 
Material  of  this  class,  though  more  often  after  treatment 
with  acid  or  other  admixture,  is  known  in  America 
as  "  tankage."  In  some  cases  a  good  deal  of  bone  is 
mixed  with  the  material  before  grinding,  and  the 
resulting  "  guano  "  approximates  to  bone  meal ;  in  other 
cases  the  nitrogenous  material  predominates.  Thus 
the  nitrogen  may  be  as  high  as  12-13  per  cent.,  in 
which  case  there  is  little  or  no  phosphate  of  lime 
present;  whereas  at  the  other  end  of  the  scale  come 
mixtures  with  4  to  5  per  cent,  of  nitrogen  and  35  to  40 
per  cent,  of  phosphate  of  lime.  A  good  representative 
example,  manufactured  by  the  Liebeg  Company  under 
the  name  of  Fray  Bentos  Guano,  contained  7  per  cent, 
of  nitrogen  and  30  per  cent,  of  phosphate  of  lime,  all 
in  a  fine  friable  condition,  dry,  and  suitable  for  sowing. 

In  its  action  and  uses  meat  is  very  similar  to  fish 
guano,  and  all  that  has  been  said  about  the  time  and 
manner  of  application  of  the  one,  equally  applies  to 


VIII.]  MEAT  RESIDUES  239 

the  other.  On  the  whole,  the  hop  growers  appear  to 
prefer  fish  to  meat  guano,  but  this  is  probably  only 
due  to  the  greater  regularity  of  the  supply  of  fish  guano 
and  its  more  uniform  composition.  There  is  no  evi- 
dence of  the  relative  superiority  of  one  over  the  other 
which  should  deter  anyone  from  buying  whichever  of 
the  two  shows  the  lower  price  per  unit  of  nitrogen  and 
phosphoric  acid.  The  price  of  the  better  grades  of 
meat  guano  is  raised  to  a  certain  extent  by  the  fact 
that  it  can  also  be  used  as  a  cattle,  and  especially  as 
a  poultry  food,  in  which  case  the  nitrogen  compounds 
always  command  a  higher  price  than  when  they  can 
only  be  employed  as  manure. 

As  with  fish  guano,  meat  guano  should  be  ploughed 
in  pretty  quickly  after  it  is  sown ;  birds  find  both 
manures  very  palatable,  and  the  rooks  in  particular  will 
carry  off  large  amounts  if  left  on  the  surface. 

Drkd  blood  is  a  product  of  the  slaughter-houses, 
which  in  its  origin  is  closely  allied  to  the  meat  guanos, 
differing  from  them  in  the  absence  of  bone  and  in 
the  nature  of  the  proteins  supplying  the  nitrogen.  As 
will  be  seen  from  its  analysis,  it  is  a  rich  fertiliser  and 
a  very  active  one,  because  of  the  readiness  with  which 
its  nitrogen  compounds  are  broken  down  into  ammonia. 

Dried  blood,  however,  comes  but  little  on  the 
market  and  is  rarely  purchased  by  the  farmer.  The 
total  production  is  small  and  it  is  practically  all  taken 
up  by  the  manure  manufacturers,  who,  because  of  its 
richness  in  organic  nitrogen  and  its  good  mechanical 
texture,  find  it  valuable  for  mixing  with  other  manures, 
when  it  is  desired  to  raise  the  percentage  of  nitrogen 
in  a  compound  manure. 

Greaves  may  be  regarded  as  a  low  grade  of  meat 
guano ;  properly  speaking  it  is  the  waste  from  tallow- 
making,  and  consists  of  the  scraps  of  cartilage  and  bone 


246  PEkUVlAN  GUANO,  ETC.  [cHAP. 

which  remain  after  the  fat  has  been  melted  down  and 
expressed  as  far  as  possible.  The  resulting  waste 
material  is  still  very  fatty,  and  contains  anything  from 
1-5  up  to  6  per  cent,  or  even  more  of  nitrogen,  with 
phosphates  varying  from  5  to  I2  per  cent,  of  phos- 
phate of  lime.  As  a  rule,  the  mechanical  condition  of 
greaves  is  bad  and  much  against  its  proper  distribution 
in  the  soil ;  the  price  is  also  often  higher  than  its 
nitrogen  content  would  warrant,  because  reasonably 
clean  samples  can  be  used  as  poultry  food.  The 
amount  of  fat  present  is  again  possibly  detrimental  to 
its  availability.  Since  greaves  is  extremely  variable 
in  its  composition,  according  to  the  kind  of  material 
which  happens  to  be  treated  at  the  factory  from  day 
to  day,  it  is  difficult  to  buy  any  large  bulk  on  a 
guarantee,  just  as  is  the  case  with  shoddy.  It  is 
difficult  also  to  judge  a  consignment  from  a  small 
sample,  so  that,  as  with  shoddy,  it  is  best  to  fix  the 
price  on  the  agreed  unit  value  for  nitrogen,  taking  the 
mean  of  several  analyses  from  the  bulk. 

Rape  dust  and  other  cake  residues. — In  the  manu- 
facture of  oil  cake  the  oil-bearing  seeds  are  subjected 
to  great  hydraulic  pressure,  either  in  bags  or  in  metallic 
moulds  which  permit  of  the  escape  of  the  oil.  The 
pressure  is  increased,  aided  sometimes  by  a  little  heat, 
until  as  much  oil  as  possible  has  been  obtained,  there 
being  left  behind  a  cake  consisting  of  the  other  parts 
of  the  seed,  the  proteins,  carbohydrates,  fibre,  etc., 
together  with  a  certain  amount  of  oil  which  cannot 
be  expressed.  The  remaining  cake  is  usually  a  valu- 
able cattle  food  and  is  sold  as  such.  In  crushing 
rape  seed,  however,  the  resulting  cake  is  apt  to  be 
very  impure ;  rape  seed  not  only  contains  a  large 
proportion  of  impurities,  but  often  also  a  good  deal 
of  wild   mustard  seed,   from  which,  when  the  cake  is 


VIII.]  RAPE  DUST  241 

used  as  food,  mustard  oil  is  generated  in  the  stomach 
to  a  dangerous  extent.  It  thus  becomes  the  custom 
only  to  use  the  purer  grades  of  rape  cake  for  cattle 
feeding ;  in  the  other  cases  the  cake  is  ground  to 
powder  and  sold  for  manure.  More  recently  a  method 
of  extracting  the  ground  rape  seed  with  carbon 
bisulphide,  in  which  the  oil  is  soluble  and  can  be 
recovered  by  distilling  off  the  solvent,  has  been  gener- 
ally adopted,  because  the  whole  of  the  oil  in  the  seed 
is  obtained  in  this  way.  The  residue,  which  is  really 
improved  by  the  complete  removal  of  the  oil,  is  only 
used  for  manure. 

Rape  dust,  as  the  ground  rape  cake  is  termed,  has 
long  been  valued  as  a  manure;  William  Ellis  in  1735 
speaks  of  oil  cake  with  approval  as  one  of  the  Hertford- 
shire "  hand  dressings  "  for  corn,  and  at  the  time  of  the 
beginning  of  scientific  agriculture  in  the  second  quarter 
of  the  last  century  we  find  that  the  use  of  rape  dust 
had  become  pretty  general  throughout  the  eastern 
counties. 

Rape  dust  contains  about  5  per  cent  of  nitrogen, 
with  such  small  quantities  of  phosphoric  acid  and  potash 
that  it  must  in  the  main  be  treated  as  a  nitrogenous 
manure.  In  its  action  it  may  be  classed  with  the  fish 
and  meat  guanos  previously  described,  in  that  decom- 
position and  nitrification  is  set  up  pretty  rapidly  and 
continues  throughout  the  whole  season.  It  has  been 
largely  used  in  the  Rothamsted  experiments,  and  the 
results  with  barley  and  mangolds  (Tables  XXVI.,  XXX., 
and  LXIII.)  show  that,  nitrogen  for  nitrogen,  it  is 
almost  as  effective  as  nitrate  of  soda  or  sulphate  of 
ammonia.  In  these  cases,  however,  the  manure  is 
applied  year  after  year  to  the  same  land,  so  that  the 
residues  unused  in  the  year  of  application  accumulate 
for    the   benefit    of    the    crop    in    future    years,  other 

Q 


242  PERUVIAN  GUANO,  ETC.  [chap. 

experiments,  however,  show  that  it  is  active  enough 
to  produce  nearly  its  full  effect  in  the  first  season. 
The  organic  matter  rape  dust  supplies  has  a  bene- 
ficial effect  upon  the  tilth  of  the  soil  ;  on  the  Rotham- 
sted  mangold  field,  as  has  been  pointed  out  earlier 
(p.  218),  the  best  results  as  regards  the  proportion  of  a 
full  plant  obtained  are  yielded  by  the  plot  manured 
with  rape  cake.  In  general  farming  rape  cake  has  been 
found  a  very  suitable  source  of  nitrogen  for  the  barley 
crop ;  it  is  highly  esteemed  by  hop  growers,  though 
of  late  years  its  comparatively  high  price  per  unit  of 
nitrogen  has  much  diminished  its  consumption  in  Kent 
and  Sussex.  It  is  also  valued  by  fruit  growers,  but  it 
is  supposed  to  make  a  bad  top  dressing  for  grass,  and, 
like  all  manures  of  its  class,  it  should  not  in  its  fresh 
condition  be  put  in  contact  with  germinating  seeds  or 
young  plants,  probably  because  of  the  fungi  and  moulds 
with  which  it  becomes  permeated  in  the  soil. 

Other  cake  residues  of  a  similar  character  come  on 
the  market  from  time  to  time  in  the  shape  of  damaged 
cargoes  of  cotton,  linseed,  or  other  cakes,  that  have  been 
spoilt  for  food  by  getting  damp  and  heating  or  by  the 
access  of  sea  water.  They  may  be  judged  on  the  same 
basis  as  rape  cake  and  their  value  estimated  from  their 
analysis. 

Castor  cake  or  pomace,  the  residue  left  after  castor 
oil  has  been  expressed  from  the  seeds,  has  no  value  for 
food,  but  makes  a  good  fertiliser  of  the  same  class  as 
rape  cake.  It  is  not  often  available  in  this  country,  as 
the  castor  oil  is  generally  expressed  before  exportation ; 
in  India  and  other  tropical  countries,  however,  it  forms 
a  very  valuable  source  of  manurial  nitrogen,  because 
organic  compounds  of  nitrogen  are  particularly  desirable 
in  tropical  soils,  which  so  rapidly  lose  their  humus  under 
cultivation. 


VIII.]  MANURES  DERI  VED  FROM  HUMAN  EXCRETA  243 


Manures  derived  from  Human  Excreta. 

Since  the  process  of  digestion  in  man  does  not 
essentially  differ  from  that  of  animals,  the  greater  part, 
and  in  the  case  of  adults  the  whole,  of  the  nitrogen* 
phosphoric  acid,  and  potash,  contained  in  human  food 
is  excreted  in  the  urine  and  fseces.  We  have  already 
seen  that  when  plants  are  grown  to  feed  animals,  the 
nutrient  constituents  drawn  from  the  soil  are  for  the 
most   part   returned   to   the  land ;   the  only   fertilising 

Table  LXXV.— Composition  of  Human  Excreta. 


Faeces. 

tJrine. 

Per  cent. 

Lb. 

per  annum. 

Per  cent. 

Lb. 

Per  annum. 

Water      . 
On:;;anic  mitter 
Ash 

Nitrogen 
Phosphoric  Acid 
Potash     . 

77-2 

19-8 

3-0 

I-O 

i-i 

0-25 

I -04 

1-3 

0-3 

96-3 
2.4 

1-3 
0-6 
0-17 

0-2 

3-2 
3-4 

constituents  which  leave  the  farm  permanently  are  the 
corn,  the  wool,  and  the  fat  stock  for  the  use  of  man. 
Even  of  these  the  husk  of  the  grain,  the  wool,  the  bones 
and  hair  find  their  way  back  to  the  land  eventually,  but 
under  modern  conditions  the  permanently  valuable  con- 
stituents of  human  food  which  pass  into  the  excreta 
are  then  wasted  agriculturally  by  being  washed  away 
into  the  rivers  and  sea.  In  the  gross  the  waste  is 
enormous  ;  the  only  difficulty  of  preventing  the  loss  lies 
in  the  fact  that  most  of  the  methods  for  rendering 
serviceable  the  wasted  material  cost  more  than  an  equal 
amount  of  fertiliser  from  some  other  extraneous  source. 
Wolff  and  Lehmann  have  estimated  (Table  LXXV.) 


244  PERUVIAN  GUANO,  ETC.  [chap. 

the  average  composition  of  human  excreta,  and  for 
the  average  yearly  output  of  each  individual,  from 
which  it  will  be  seen  that  neither  urine  nor  faeces  are 
particularly  rich  fertilisers. 

These  are  mean  figures  for  all  ages,  and  the  weights 
of  nitrogen  and  phosphoric  acid  excreted  per  annum 
are  calculated  upon  a  somewhat  different  basis ;  for 
adults  the  quantities  should  be  at  least  half  as  large 
again.  But  taking  high  average  figures,  an  adult  only 
excretes  during  a  year  about  12  lb.  of  nitrogen,  7  of 
phosphoric  acid,  and  5  of  potash,  worth  respectively 
about  7s.  6d.,  2s.,  and  is.,  or  los.  6d.  a  year  in  all  when 
converted  into  a  marketable  fertiliser.  Though  for  a 
large  population  the  total  waste  may  thus  seem  to  be 
enormous,  los.  6d.  per  head  is  yet  but  a  small  amount 
to  be  set  against  the  expense  of  dealing  with  such 
a  quantity  of  low  grade  material  so  difficult  to 
handle. 

Many  attempts  have  naturally  been  made  to  utilise 
the  fertilising  material  contained  in  human  excreta ;  on 
the  crowded  lands  of  China  it  is  applied  fresh  to  the  soil 
and  is  daily  fetched  by  hand  from  the  cities  for  that 
purpose,  but  such  a  mode  of  dealing  with  night  soil  is 
only  possible  with  an  excessively  low  standard  of  living. 
In  the  towns  of  Flanders  and  the  north  of  France  it 
was  the  custom  to  collect  the  excreta  in  large  tanks, 
and  after  fermentation,  to  cart  them  out  in  a  liquid  form 
to  the  fields,  though  modern  views  on  public  health  are 
rapidly  getting  rid  of  such  practices.  Almost  the  only 
method  of  getting  human  excreta  back  to  the  land 
cheaply  and  inoffensively  is  in  houses  or  small  com- 
munities where  the  "  earth  closet "  system  prevails. 
There  the  excreta  are  mixed  with  dry  sifted  earth, 
which  deodorises  them  quickly  and  completely,  the 
mixture  is  removed  daily  to  a  heap  under  cover,  and 


VIII.]    MANURES  DERIVED  FROM  NIGHT  SOIL        245 

in  a  very  short  time,  the  faecal  solids,  paper,  etc.,  are  so 
completely  broken  down  by  bacterial  decay  that  the 
soil  can  be  spread  upon  the  land  and  used  for  growing 
crops. 

In  some  towns  attempts  have  been  made  to  manu- 
facture a  concentrated  fertiliser  by  collecting  human 
excreta  without  any  admixture  and  evaporating  off  the 
water,  sometimes  with  the  addition  of  a  little  acid  to 
fix  the  ammonia  arising  from  the  urea,  sometimes  with 
powdered  turf,  etc.,  to  give  the  finished  material  a 
better  mechanical  texture.  In  Rochdale,  one  of  the  towns 
where  such  a  system  prevails,  the  houses  are  provided 
with  external  pan  closets  and  the  faeces  are  collected 
at  short  intervals  for  conveyance  to  the  manure  works. 
The  following  analysis  shows  the  composition  of  the 
resulting  manure — 


Water         .... 

.       13-9 

Organic  matter . 

.      637 

Containing  Nitrogen 

6-74 

Phosphoric  Acid 

3-12 

Potash        .... 

2-l6 

Insoluble  Ash    . 

3-45 

The  almost  universal  prevalence  of  a  water-borne 
system  of  dealing  with  excreta  puts  an  end  to  all  such 
systems  and  intensifies  the  difficulty  of  saving  the 
fertilising  constituents  of  human  food  for  the  land 
again,  because  of  the  enormously  increased  dilution 
they  have  experienced  ;  the  sewage  from  towns  with 
water-closets  only  contains  on  the  average  about  2-2 
parts  of  nitrogen  per  100,000.  Where  the  conditions 
are  favourable  and  the  community  has  at  hand  a 
sufficient  area  of  light,  permeable  land  which  can  be 
cheaply  graded  and  adapted  to  irrigation,  then  the 
sewage  waters,  either  with   or  without   a  preliminary 


246  PERUVIAN  GUANO,  ETC.  [chap. 

treatment  to  get  rid  of  suspended  matter,  can  be 
profitably  utilised  in  raising  crops.  But  light  land, 
permitting  of  free  percolation,  is  necessary,  and  it  must 
not  be  overloaded  with  sewage  but  allowed  intervals 
for  aeration  and  oxidation,  or  else  the  surface  becomes 
sealed  with  a  layer  of  organic  matter  difficult  to  break 
down  and  both  percolation  and  purification  cease.  An 
acre  of  land  is  not  capable  of  dealing  with  the  sewage 
of  many  more  than  one  hundred  people.  This  is  hardly 
the  occasion  to  discuss  the  various  processes  now  in 
vogue  for  the  purification  of  sewage  by  bacterial  action 
or  by  land  filtration,  but  at  one  point  they  do  touch  the 
manure  question  by  turning  out  "  sewage  sludges " 
which  possess  a  certain  fertilising  value.  In  many 
of  the  processes  the  raw  sewage  is  first  submitted  to 
some  process  of  chemical  precipitation  to  effect  the 
removal  of  the  suspended  matter  and  obtain  a  clear 
effluent,  which  can  be  purified  by  bacterial  filter  beds 
or  by  application  to  the  land.  As  precipitating  agents, 
lime,  alum,  and  sulphate  of  iron  are  commonly  employed, 
alone  or  together,  the  object  being  to  produce  a  bulky 
colloidal  precipitate  which  will  entangle  and  drag  down 
the  flocculent  organic  matter  of  the  sewage.  After 
mixing  with  the  precipitant,  the  sewage  is  left  in  tanks 
to  settle,  the  clear  liquid  is  passed  on  for  further  treat- 
ment, and  the  remaining  sludge  is  freed  from  excess  of 
water  by  passing  through  some  form  of  pressure  filter. 
The  resulting  press  cakes  are  either  disposed  of  locally 
in  the  wet  state  or,  in  one  case  at  least,  dried  and  sold 
as  a  manure  under  the  name  of  "  native  guano."  It  is 
obvious  that  any  such  precipitating  process  with  either 
lime  or  the  sulphates  of  alumina  and  iron,  can  only  take 
out  of  the  sewage  such  nitrogenous  bodies  as  proteins, 
leaving  the  greater  part — the  amides  and  ammonium 
salts,  still  in  solution.     Thus  the  sludge  will  only  con- 


VIII.] 


SEWAGE  SLUDGES 


247 


tain  the  smaller  and  least  valuable  portion  of  the 
nitrogenous  material,  also  the  phosphates  but  not  the 
potash  of  the  sewage.  Table  LXXVl.  gives  a  series  of 
analyses  of  such  sludges,  made  for  the  Royal  Commis- 
sion on  Sewage  Disposal  in  1906,  which  may  be  taken 
as  typical  of  this  class  of  material : — 

Table  LXXVL— Composition  of  Sewage  Sludges. 


1 

2 

3 

4 

Water         .... 

lO'I 

31-2 

40-6 

3-55 

Organic  matter,  etc.   . 

49.8 

24-9 

i6-8 

38-23 

Nitrogen    .... 

2-32 

0-94 

0-55 

1-65 

Phosphoric  Acid 

2-27 

o-8o 

1-42 

1-25 

Lime 

2-34 

24-6 

24-45 

8-40 

Potash         .... 

traces 

traces 

traces 

traces 

Insoluble  matter 

23-27 

7 -06 

5-57 

28-28 

Of  these  sewage  sludges  No.  i  represents  the 
material  sold  as  "native  guano,"  2  and  3  are  lime 
sludges,  while  for  4  the  precipitant  had  chiefly  been 
sulphates  of  iron  and  alumina.  It  will  be  seen  that  in 
no  case  is  the  material  possessed  of  much  fertilising 
value,  for  not  only  are  the  percentages  of  nitrogen  and 
phosphoric  acid  low,  but  they  must  be  combined  in 
extremely  inactive  forms.  Field  trials  show  that  the 
action  of  these  sludges  as  manures  is  very  small,  below 
that  of  equivalent  amounts  of  nitrogen  and  phosphoric 
acid  in  commercial  fertilisers,  so  small  in  fact  to  be 
negligible  unless  the  material  is  applied  in  very  large 
quantity.  Indeed,  we  can  only  conclude  that  these 
sludges  possess  little  or  no  value  as  fertilisers,  though 
they  may  be  valuable  for  the  lime  they  contain,  especi- 
ally on  light  sandy  land  where  they  will  also  add  some 
water-retaining  humus  and  improve  the  texture  of  the 
soil. 


248 


PERUVIAN  GUANO,  ETC.  [chap.  viii. 


Table  LXXVIL— Composition  of  Guanos  and  Kindred 
Fertilisers. 


a 

0 

0 

« 

0  . 

St,  « 

A 

^ 

.a -a 

S.S,A 

^ 

0 

§0 

>2§ 

1 

0 

g 

A 

d  tv  ja 

Ph 

^ 

^HP. 

Peruvian  Guano 

Ballestas,  1902  . 

I2'24 

11-36 

24-76 

fi 

Macabi,     1902  . 

IO-57 

13-90 

30-30 

II 

Guanape,  1902  . 

7-75 

I8-S9 

34-00 

.•• 

*.. 

>i 

Lobos,       1902  . 

2-86 

29-52 

64-35 

ti 

„            1902  . 

I-50 

31-63 

68-95 

.... 

II 

1906  . 

8-4 

13-17 

28-70 

2"8S 

II 

„           1906  . 

4.9 

21-22 

46-25 

3-51 

II 

„            1906  . 

2-37 

2I.6l 

47-12 

2.90 

)> 

Equalised  . 

7-8 

II — 14 

25—30 

2—3 

... 

Ichaboe        . 

. 

8-64 

12-14 

28-09 

2-47 

... 

)) 

•         •        . 

8-22 

14-3 

31-3 

2.0 

... 

Damaraland 

«         .         • 

6.83 

14.63 

31-89 

Fish  Meals  . 

• 

8-97 

8.87 

19-34 

4.96 

11            * 

• 

8^8 

10-14 

22-11 

8.48 

„          (from 
)>            • 

)»            • 

>)            • 

herring  refuse)  . 

8.78 
9-29 
6-26 
6.15 

6-59 
7-70 
5-96 
5-26 

14-37 
16-79 
12.99 
11-47 

... 

16.46 

Meat  Meals  . 

•        •        .        . 

12-3 

0-92 

2-0 

f)         • 

• 

6-51 
6-36 

13-22 
14-32 

28-82 
31-27 

)i         • 

. 

5-82 

12-80 

27-94 

»         • 

•        • 

5-6i 

11-35 

24-77 

... 

... 

Greaves        , 

. 

6-22 

4-19 

2.6l 

5-48 

2-l8 

2-56 

11-96 

4-75 
5-50 

Dried  Blood 

•                 •                 •                 • 

9-65 

0-83 

1-82 

Rape  Dust  (Homco)     . 

4-84 

1-7 

3-8 

" 

•                 •                 •                 • 

5 -08 

1-58 

3-44 

Damaged  Cotton  Cake 

4-78 

1-73 

3-77 

2-77 

Castor  Cake 

• 

^■" 

1.83 

3-99 

1.04 

CHAPTER  IX 

MATERIALS    OF    INDIRECT    FERTILISING   VALUE 

Lime — Early  Use  of  Lime — White  and  Grey  Limes — Lime 
Ashes — Marl — Chalk — Ground  Limestone — Indications  of  the 
Lack  of  Lime  in  the  Soil — Action  of  Lime  upon  the  Soil — 
Improvement  of  Texture — Promotion  of  the  Oxidation  of 
Nitrogenous  Residues  in  the  Soil — Increase  in  the  Availability 
of  Phosphoric  Acid  and  Potash — General  Action  of  Soluble 
Salts  on  the  Soil — Gas  Lime — Gypsum — Salt — Sulphate  and 
Carbonate  of  Magnesia — Sulphate  of  Iron  ;  Supposed  Connec- 
tion of  Iron  in  the  Soil  with  the  Colour  of  Fruit  and  Flowers 
— Manganese  Salts — Silicates — Green  Manuring — Folding 
Catch  Crops  on  the  Land. 

There  are  several  substances  commonly  used  by 
farmers  as  manures,  which  produce  desirable  effects 
upon  the  crops,  although  they  are  not  themselves  plant 
foods  and  only  act  indirectly  on  the  soil,  either  by 
making  it  more  amenable  to  cultivation  or  by  bringing 
into  action  the  stored-up  reserves  in  the  soil. 

Such  substances  are  lime,  gypsum,  salt,  all  of  which 
contain  elements  present  in  the  plant,  though  they  also 
exist  in  the  soil  in  quantities  sufficient  for  the  nutrition 
of  the  crop ;  they  are  valuable  as  soluble  salts  for  their 
indirect  effect  in  making  soluble  other  more  important 
plant  foods  in  the  soil. 

Lime. — When  the  value  of  lime  became  known  it 
is  impossible  to  ascertain,  but  we  find  that  the  use  of 
both  lime  and  marl  was  recognised  among  the  Romans. 


2SO  MATERIALS  OF  INDIRECT  VALUE         [chap. 

For  example,  Pliny  writes  : — "  There  is  another  way 
of  nourishing  earth  by  earth,  which  has  been  found  out 
in  Britain  and  Gaul.  It  is  thought  that  there  is  a 
greater  degree  of  fruitfulness  in  this  kind  than  in  any 
other.  It  is  a  certain  richness  of  earth,  like  the  kernels 
in  animal  bodies,  that  are  increased  by  fatness.  "  The 
principal  of  those,  reckoned  the  fat  kinds,  is  the 
white ;  of  this  there  are  many.  One  very  acrid,  that 
has  already  been  mentioned.  Another  kind  of  the 
white  is  like  a  soft  clay.  It  is  found  at  a  great  depth ; 
the  pits  very  frequently  dug  an  hundred  feet  down, 
narrow  at  the  mouth ;  but  the  vein,  as  in  metals, 
widening  within.  This  is  chiefly  used  in  Britain.  It 
remains  eighty  years ;  nor  is  there  an  instance  of  any 
man  laying  it  twice  on  the  same  field.  "The  Hedui 
and  Pictones  manure  their  fields  with  lime,  which  is 
likewise  found  very  good  for  olives  and  vines.  All 
marl  ought  to  be  laid  upon  ploughed  land,  that 
its  virtue  may  be  the  easier  sucked  in  by  the  soil.  A 
little  dung  should  be  laid  on  with  it,  particularly  with 
that  kind  that  at  first  is  too  hard,  and  does  not  dissolve 
well  enough  to  nourish  plants.  Besides,  of  whatever 
kind  it  is,  it  hurts  the  soil,  by  its  being  new,  and  does 
not  render  it  fertile  till  after  the  first  year." 

The  regular  use  of  some  form  of  lime  or  chalk  was 
part  of  the  accepted  routine  of  farming  as  early  as  we 
possess  any  records  of  British  agriculture,  and  among 
the  manures  it  figures  in  all  books  of  the  sixteenth  and 
seventeenth  centuries.  In  fact  "the  black  and  the 
white,"  dung  and  lime,  were  the  only  manures  employed 
by  the  great  mass  of  farmers  until  well  into  the 
nineteenth  century. 

Lime  itself,  or  quicklime,  is  obtained  by  the  "  burning  " 
of  any  form  of  calcium  carbonate,  which  occurs  as 
limestone  [either  pure  in  the  Mountain  Limestone  of 


IX.]  VARIETIES  OF  LIME  251 

Derbyshire  and  North  Yorkshire,  or  argillaceous  in  the 
Lias]  as  chalk,  and  even  as  shell  sand,  on  the  Cornish 
and  other  coasts.  The  so-called  "  burning  "  consists  in 
driving  off  by  heat  the  carbonic  acid  contained  in  the 
calcium  carbonate.  The  resulting  lime,  known  some- 
times as  quicklime,  stone  lime,  cob  lime,  lime  shells, 
etc.,  combines  with  great  readiness  with  water,  developing 
much  heat  and  falling  down  into  a  fine  powder  termed 
"  slaked  lime,"  and  this  slaked  lime  will  then  combine 
with  the  carbonic  acid  present  in  the  atmosphere  to 
reconstruct  the  original  carbonate  of  lime.  Thus  when 
lime  is  applied  to  the  soil  it  very  rapidly  becomes 
carbonate  and  the  effects  of  "  liming  "  are  really  due  to 
carbonate  of  lime. 

The  quality  of  lime  varies  considerably,  according 
as  it  has  been  made  from  a  pure  limestone  or  from  the 
impure  forms  containing  some  admixture  of  clay  and 
sand.  In  the  former  case  the  result  is  a  white,  "  fat," 
lime  which  swells  considerably  on  slaking  and  falls 
into  a  very  fine  powder ;  the  other  grey  or  thin  limes 
do  not  slake  so  readily  nor  swell  much,  they  also 
contain  a  smaller  proportion  of  free  lime  and  are  less 
valuable  for  agricultural  purposes.  In  some  parts  of 
the  country  the  limestone  is  dolomitic  and  contains 
considerable  proportions  of  magnesium  carbonate,  but 
the  limes  arising  from  it  are  not  regarded  with  so  much 
favour  by  farmers. 

Lime  ashes,  which  are  to  be  had  cheaply  in  the 
neighbourhood  of  the  kilns,  consist  of  the  waste 
accumulating  in  burning  the  lime  and  are  therefore 
mixtures  of  lime  in  a  powder  with  the  ashes  of  the 
coal  employed.  The  percentage  of  lime  may  vary  from 
20  to  60  according  to  circumstances,  so  that  the  value 
of  each  lot  must  be  judged  by  its  apparent  cleanliness 
and  freedom  from  clinker. 


252  MATERIALS  OF  INDIRECT  VALUE         [cHAP. 

Since  lime  becomes  calcium  carbonate  in  the  soil, 
obviously  the  same  results  would  be  obtained  by 
applying  the  latter  material,  the  main  advantage  in  the 
use  of  lime  lies  in  the  very  fine  state  of  division  into 
which  it  falls  on  slaking  and  the  consequent  good 
admixture  with  the  soil  that  is  effected. 

Such  a  finely  divided  calcium  carbonate  is  provided 
in  many  parts  of  the  country  by  the  calcareous  marls 
which  occur  in  beds  sufficiently  near  the  surface  to 
admit  of  working,  as  in  the  New  Red  Sandstone 
formations  in  Cheshire,  Worcester,  etc.,  or  the  shell 
marls  which  occur  in  Norfolk,  A  true  marl  is  a  clay 
containing  a  variable  percentage  of  calcium  carbonate> 
it  is  specially  valuable  on  sandy  or  peaty  soils,  not  only 
for  its  calcareous  matter  but  also  for  the  clay,  which 
improves  the  texture  of  the  soil. 

In  many  parts  of  the  country,  where  the  superficial 
formations  resting  upon  the  Chalk  are  \  devoid  of 
carbonate  of  lime,  it  was  formerly  the  custom  to  sink 
bell  pits  into  the  chalk  rock,  haul  it  up  in  baskets  and 
spread  it  upon  the  surface.  In  Hertfordshire,  for 
example,  this  chalking  was  part  of  the  regular  routine 
of  farming  from  the  earliest  times  of  which  we  have 
records,  and  from  the  analyses  of  the  Rothamsted  soils 
it  has  been  ascertained  that  by  the  repetition  of  the 
process  a  hundred  tons  per  acre  or  more  must  have 
been  applied  before  the  beginning  of  the  nineteenth 
century,  there  being  now  present  in  the  soil  from 
2  to  5  per  cent,  of  carbonate  of  lime,  all  of  artificial 
origin.  Chalk  was  also  formerly  carried  for  con- 
siderable distances  on  to  the  clay  formations  —  the 
London  Clay,  the  Gault  Clay,  and  the  Weald  Clay — 
that  are  contiguous,  but  the  increased  cost  of  labour 
has  put  an  end  to  this  practice. 

None  of  the  other  British  limestones  are  sufficiently 


IX.]  C ROUND  LIME  AND  LIMESTONE  253 

soft  to  allow  of  their  direct  application  to  the  land  with 
any  prospect  of  their  reduction  to  a  fine  state  by  the 
action  of  the  weather,  but  of  late  years,  since  many  of 
the  lime  works  have  established  grinding  plants,  it  has 
been  possible  to  obtain  both  limestone  and  chalk  in  a 
finely  ground  condition.  In  certain  parts  of  the  country 
precipitated  carbonate  of  lime  in  a  very  fine  state  of 
division  is  to  be  obtained  from  water  works  which 
soften  their  hard  calcareous  water  by  the  use  of  lime, 
and  this  forms  valuable  material  for  all  land  in  need  of 
lime.  Ground  quicklime  is  also  manufactured  and  forms 
a  very  convenient  means  of  applying  small  quantities  of 
lime  to  the  soil ;  unfortunately  the  ground  lime  avail- 
able is  generally  grey  or  cement  lime,  so  that  at  its 
higher  price  and  with  its  lower  proportion  of  pure  lime 
it  is  often  more  profitable  to  buy  a  larger  quantity  of 
ordinary  lime.  When  the  practice  of  liming  was  more 
general  it  was  customary  to  apply  very  large  amounts, 
4  to  6  or  8  tons  per  acre  (100  to  200  bushels)  at  long 
intervals,  but  this  is  likely  to  act  injuriously  by  causing 
too  rapid  oxidation  in  the  soil  at  first,  and  a  better  plan 
is  to  put  on  I  ton  or  so  of  ordinary  lime  every  time  the 
turnip  crop  comes  round  in  rotation,  or  5  to  10  cwt.  of 
ground  lime  to  each  crop  for  which  artificial  manures 
are  applied.  A  heavy  dressing  of  lime  is  also  supposed 
to  affect  the  processes  of  nitrification  detrimentally  for 
some  time  after  its  application. 

Lime,  chalk,  or  ground  limestone,  in  whatever  form 
it  is  used,  should  always  be  applied  to  the  land  as  early 
in  the  winter  as  may  be  convenient,  on  arable  land 
before  ploughing. 

The  question  of  whether  lime  is  required  as  a  regular 
part  of  the  routine  of  farming  on  a  given  soil  can  only 
be  decided  by  an  analysis  of  the  soil ;  any  soil  contain- 
ing less  than   i  per  cent,  of  calcium  carbonate  will  be 


^54  MATERIALS  OF  INDIRECT  VALUE         [chap. 

benefited  by  liming,  and  when  the  percentage  falls 
to  \  per  cent,  lime  becomes  a  necessity  to  enable  the 
manures  to  exert  their  proper  action. 

Many  clays  and  sands  are  in  this  latter  condition ; 
and  although  the  absence  of  lime  may  often  be  con- 
cluded from  the  appearance  of  the  vegetation,  every 
farmer  ought  to  get  a  determination  made  of  the 
amount  of  carbonate  of  lime  in  his  soil,  because  the 
whole  scheme  of  manuring  should  depend  on  whether 
the  soil  is  properly  supplied  with  a  base. 

In  arable  land  the  presence  of  the  small  sorrel 
{Rumex  acetosella),  corn  marigold  {Chrysanthemtini 
segetuni),  Spurrey  {Spergula  arvensis)^  and  the  growth 
of  foxglove  {Digitalis  purpurea)  and  bracken  {Pteris 
aquilind)  on  the  waste  places  are  pretty  sure  signs  of 
the  absence  of  lime,  while  the  pastures  on  such  soils  are 
generally  very  deficient  in  leguminous  herbage.  If  a 
little  soil  when  covered  with  dilute  hydrochloric  acid 
shows  no  visible  effervescence,  the  proportion  of 
carbonate  of  lime  must  be  below  what  is  desirable  for 
the  healthy  growth  of  vegetation.  Nor  must  it  be 
supposed  that  the  use  of  artificial  manures,  such  as 
superphosphate  of  lime,  or  bones  which  are  phosphate 
of  lime,  or  gypsum  which  is  sulphate  of  lime,  will 
obviate  the  necessity  of  liming.  Lime  or  its  carbonate 
are  needed  in  the  soil  to  supply  a  free  base,  and  in 
the  compounds  mentioned  it  is  already  saturated  with  a 
fixed  acid  ;  in  fact,  in  superphosphate  of  lime  there  is  an 
excess  of  acid,  so  that  this  fertiliser  reduces  the  amount 
of  carbonate  of  lime  in  the  soil.  Gas  lime  is  again  of 
very  little  service  in  this  connection,  since  the  base  has 
already  been  largely  combined  with  various  compounds 
of  sulphur,  and  still  remains  so  after  these  sulphur 
compounds  have  been  oxidised  by  exposure  of  the  gas 
lime  for  some  time.     The  following  table  (LXXVIII.) 


IX.j 


ACTION  OF  LIME 


255 


shows  analyses  of  "  grey  "  and  "  white  "  limes  made  from 
chalk  : — 

Table  LXXVIII.— Analysis  of  Lime. 


White  Lime. 

Grey  Lime. 

Caustic  Lime     .         .         • 
Carbonate  of  Lime    .        . 
Magnesia  .... 
Oxide  of  Iron    . 
Alumina    .... 
Silica  as  Soluble  Silicates. 
Insoluble  residue      .        , 
Water,  Alkalis,  etc  . 

90-20 
2-40 

0-35 
0-52 
1-70 

2 -60 

0-25 
1.98 

74 -DO 

2-66 

0.38 

I -GO 

7 -60 
8 -60 
0.94 
4-82 

Total        , 

roO'OO 

lOO-OO 

Lime  is  best  applied  to  the  stubbles  in  the  autumn 
before  ploughing  in  preparation  for  a  root  crop ;  if 
ground  lime  is  used  it  may  be  sown  broadcast  with  any 
form  of  manure  distributor,  choosing  a  quiet  morning 
while  the  dew  is  still  on  the  surface. 

Stone  lime  should  be  distributed  in  small  heaps, 
covered  with  a  little  earth  and  left  for  a  week  or  two  to 
slake,  under  which  conditions  it  will  fall  into  a  fine 
powder.  The  heaps  are  then  broken  down  and  thrown 
abroad  before  ploughing. 

The  action  of  lime  is  partly  physical,  affecting  the 
texture  of  the  soil,  and  partly  chemical,  setting  free  the 
dormant  reserves  of  plant  food. 

On  the  strong  soils  the  physical  action  of  lime  is 
most  manifest ;  it  acts  by  flocculating  the  finest  clay 
particles,  causing  them  to  aggregate  into  temporarily 
larger  units,  and  so  making  the  soil  effectively  of  coarser 
texture.  The  soil  thus  becomes  less  retentive  of 
moisture ;  percolation  is  increased,  making  the  limed 
land  dryer  and  warmer,  so  that  it  admits  of  cultivation 
earlier  in  the  spring  and  is  far  more  friable  when  dry. 


2S6  MATERIALS  OF  INDIRECT  VALUE         [CHAP. 

In  dry  seasons  the  clay  will  crack  less  and  the  crop 
will  keep  on  growing  longer,  because  the  improved 
texture  of  the  soil  admits  of  a  better  supply  of  subsoil 
water  to  the  plant  by  surface  tension. 

It  is  difficult  to  exaggerate  the  improvement  that 
lime  effects  in  the  dryness  and  workability  of  strong 
soils,  which  in  many  cases  would  not  be  fit  for  arable 
cultivation  had  they  not  been  so  treated.  It  has 
already  been  mentioned  that  on  the  Rothamsted 
estate  the  custom  of  chalking  has  added  from  2  to 
5  per  cent,  of  carbonate  of  lime  to  the  surface  soil, 
which  is  otherwise  non-calcareous ;  but  on  one  of  the 
fields,  formerly  under  experiment,  the  treatment  had 
never  been  carried  out.  This  field,  Geescroft,  formerly 
carried  experimental  crops  of  oats  and  beans,  but  during 
the  rainy  seasons  about  1879  the  land  lay  so  persis- 
tently wet  in  the  spring  that  on  several  occasions  a 
tilth  could  not  be  obtained  in  time  for  sowing,  and  the 
land  had  to  lie  fallow,  until  at  last  cultivation  was 
abandoned  and  the  field  was  allowed  to  fall  down  into 
grass.  Even  now  the  herbage  is  very  inferior  and 
shows  the  wet  character  of  the  soil  by  the  prevalence 
of  Aira  ccsspitosa ;  yet  in  situation,  drainage,  and 
mechanical  composition  this  soil  is  in  no  respects 
different  from  that  of  the  other  Rothamsted  fields. 
The  essential  factor  which  has  caused  all  the  difference 
in  the  character  of  the  two  soils  is  the  absence  of  calcium 
carbonate  from  the  Geescroft  field,  which  for  some  reason 
had  escaped  the  chalking  given  to  the  other  fields.  The 
physical  improvement  of  a  clay  soil  by  lime  is  not  appar- 
ent at  once  but  grows  from  year  to  year  after  the  applica- 
tion of  the  lime ;  the  flocculating  action  is  really  not  due 
to  the  lime  itself  but  to  the  soluble  calcium  bicarbonate 
which  arises  from  the  action  of  water  and  carbonic  acid 
upon  the  calcium  carbonate  formed  from  the  lime. 


IX.]  ACTION  OF  LIME  257 

On  the  lighter  soils — the  sands  and  gravels — lime 
exerts  a  good  effect  by  forming  a  weak  cementing  agent 
and  increasing  the  cohesion  of  the  particles.  As  a  rule, 
however,  it  is  not  wise  to  apply  quicklime  in  any 
quantities  to  very  light  open  soils,  because  oxidation  of 
the  organic  matter  is  pushed  on  too  rapidly.  Either 
chalk  or  marl,  or  some  form  of  calcium  carbonate  should 
be  used,  or  the  quicklime  should  only  be  applied  in 
small  quantities. 

From  the  chemical  side  the  great  value  of  carbonate 
of  lime  in  the  soil  lies  in  its  power  of  maintaining 
the  neutral  reaction  necessary  to  the  development 
of  those  bacteria  which  oxidise  the  organic  compounds 
in  the  soil  to  the  state  of  plant  food.  In  the  absence  of 
lime,  organic  matter  by  its  decay  gives  rise  to  various 
acid  bodies  which  may  be  grouped  as  humic  acid,  and 
the  acidity  thus  produced  inhibits  the  action  of  many  of 
the  valuable  groups  of  bacteria,  such  as  the  Azotobacter 
which  fix  nitrogen,  and  the  nitrifying  bacteria  which 
convert  ammonia  into  nitrates.  It  has  been  shown  that 
in  soils  that  are  acid  through  the  accumulation  of  humic 
acid,  nitrification  is  at  a  standstill  and  bacterial  life  gener- 
ally is  repressed  in  favour  of  the  growth  of  moulds  and 
micro-fungi,  which  compete  actively  with  the  crop  for 
the  plant  food  in  the  soil. 

On  all  land  which  has  been  enriched  by  the 
residues  of  past  manuring  or  by  the  debris  of  previous 
vegetation,  lime  is  very  necessary  to  promote  the 
oxidation  of  the  nitrogen  compounds  and  the  formation 
of  nitrates  for  the  crop ;  consequently  it  is  on  bog  or 
peaty  land,  on  old  turf  or  reclaimed  forest  land,  or  on 
old  gardens,  that  liming  exercises  its  maximum  effect. 
The  following  figures  (Table  LXXIX.)  show  the  com- 
parative crops  on  limed  and  unlimed  plots,  otherwise 
manured   alike,   in   an   old   hop   garden   at    Farnham, 


258 


MATERIALS  OF  INDIRECT  VALUE        [chap. 


Surrey,  which  had  been  heavily  dressed  with  organic 
manures  for  many  years  previously  : — 

Table  LXXIX.— Effect  of  Lime  upon  Hop  Soils. 


Artificial  Manures. 

Year. 

With  1  ton  Lime 
per  acre. 

With  no  Lime. 

1895 

100 

70 

1896 

100 

84 

1897 

100 

80 

1900 

ICO 

81 

1 901 

100 

90 

Because  of  the  wide  fluctuations  due  to  season  the 
yield  each  year  has  been  calculated  on  a  basis  of  the 
limed  plot  =  100,  showing  that,  on  the  average,  liming 
has  increased  the  return  by  19  per  cent. 

It  is  on  soils  with  a  tendency  to  sourness  that 
liming  is  of  the  greatest  value,  for  in  such  cases  dung 
or  any  other  organic  manure  only  tends  to  aggravate 
the  evil.  This  is  very  well  illustrated  by  the  action  of 
lime  upon  the  grass  plots  at  Rothamsted,  where  2000 
lb.  per  acre  of  ground  lime  was  applied  to  half  of  the 
plots  in  January  1903,  with  the  results  shown  in  Table 
LXXX. ;  the  yield  of  the  limed  half  of  the  plot  in  each 
year  has  been  compared  with  the  yield  of  the  unlimed 
portion  taken  as  100. 

It  will  be  seen  that  the  increased  yield  due  to 
liming  is  most  manifest  on  plots  4/2,  9,  and  ii/i, 
where  the  soil  had  become  acid  through  the  long- 
continued  use  of  ammonium  salts.  It  should  also  be 
noticed  that  the  action  of  lime  is  slow,  and  is  more 
manifest  in  the  third  and  fourth  year  after  its  applica- 
tion than  in  the  first  and  second. 

It  has  already  been   stated  that  moulds  and  other 


IX.] 


ACTION  OF  LIME 


259 


micro-fungi  are  favoured  by  an  acid  reaction  in  the 
soil,  consequently  we  find  that  various  fungoid  diseases 
of  plants  are  specially  prevalent  on  soils  devoid  of 
calcium  carbonate,  a  notable  example  being  the  slime 
fungus,  PlasiiiodiopJiora  brassiccB,  which  causes  "  finger- 
and-toe,"  "  club  root,"  or  "  anbury  "  in  turnips,  cabbages, 

Table  LXXX.— Effect  of  Lime  upon  Rothamsted  Grass  Plots 
(Unlimed  =  ioo). 


Plot. 

1903. 

1904. 

1905. 

1906. 

1907. 

3 

Unmanured  . 

154 

134 

119 

98 

119 

4/2 

Super,  and  Am. -salts 

124 

III 

134 

118 

113 

7 

Complete  Minerals 

105 

100 

106 

120 

no 

8 

Minerals  ;  no  Potash     . 

93 

90 

103 

93 

no 

9 

As  7,  +Am.-salts  . 

121 

no 

142 

128 

106 

ii/r 

As  7,  +extra  Am. -salts  . 

115 

103 

206 

120 

167 

10 

As  8,  +Am.-salt5  . 

120 

III 

128 

112 

104 

and  similar  plants.  This  disease  does  not  occur  on  cal- 
careous soils  and  can  be  obviated  on  soils  where  it  does 
prevail  by  a  thorough  liming,  best  applied  both  after 
the  removal  of  one  turnip  crop  and  again  immediately 
before  another  is  sown.  As  long  an  interval  as  possible 
should  elapse  between  the  two  cruciferous  crops  to 
enable  the  spores  of  the  disease  to  die  off  in  the 
soil,  now  rendered  faintly  alkaline.  The  finger-and- 
toe  fungus  is  not  the  only  one  thus  affected  by  lim.e, 
but  it  is  the  one  known  on  the  widest  scale ;  speaking 
generally,  calcareous  so'Is  are  always  the  healthiest  for 
crops. 

But  the  nitrogenous  compounds  in  the  soil  are  not 
the  only  ones  rendered  more  available  by  the  presence 
of  carbonate  of  lime ;  both  phosphoric  acid  and  potash 
are  thereby  kept  or  brought  into  a  more  soluble  form. 
When  soluble  phosphates  are  applied  to  the  land  they 
are  precipitated  either   as   di-calcium  phosphate,  ferric 


26o  MATERIALS  OF  INDIRECT  VALUE        [chap. 

phosphate,  or  aluminium  phosphate ;  and  on  soils 
containing  any  reasonable  amount  of  calcium  carbonate 
the  former  will  predominate,  the  two  latter  on  the  sands 
and  clays  where  calcium  carbonate  is  lacking.  Now  the 
effective  solubility  of  the  two  latter  phosphates  in  the 
soil  water  is  very  much  below  that  of  the  precipitated 
calcium  phosphate,  consequently  their  phosphoric  acid 
is  much  slower  in  reaching  the  plant,  which  may  remain 
short  of  this  necessary  constituent  even  though  large 
amounts  have  been  applied  to  the  soil.  Similarly  a 
soil  may  contain  considerable  amounts  of  phosphoric 
acid,  which  in  the  absence  of  lime  is  combined  with 
ferric  oxide  or  alumina  so  as  to  be  in  a  highly 
insoluble  condition;  for  example,  a  soil  derived  from 
the  marlstone  has  been  known  to  contain  0-84  per  cent, 
of  phosphoric  acid  but  yet  show  great  response  to 
phosphatic  manures,  because  at  the  same  time  it  con- 
tained 28-16  per  cent,  of  ferric  oxide  and  no  calcium 
carbonate.  Applications  of  lime  or  calcium  carbonate 
are  of  great  value  on  these  soils  because  they  form  a 
certain  amount  of  calcium  phosphate  by  interaction  with 
the  iron  or  aluminium  phosphates,  and  so  increase  the 
proportion  of  phosphoric  acid  in  the  soil  water. 

The  action  of  lime  upon  the  potash  compounds  in 
the  soil  is  equally  marked ;  as  the  soil  water  carries 
down  the  dissolved  calcium  bi-carbonate  it  attacks  the 
zeolitic  double  silicates  in  the  clay  and  some  of  their 
soluble  bases,  potash  among  them,  change  place  with 
the  lime  and  come  into  solution.  Thus  lime  is  precipi- 
tated and  potash  is  found  in  the  soil  water.  The  action 
is  the  converse  of  that  which  takes  place  when  potash 
salts  are  applied  as  manures ;  whatever  base  is  in  excess 
in  the  water  reaching  the  soil  will  turn  the  others  out 
and  be  precipitated  in  the  solid  zeolite.  When  potash 
salts  are  applied  to  the  land  the  strong  solution  thus 


IX.]  ACTION  OF  LIME  261 

formed  attacks  the  zeolites  and  replaces  calcium  by- 
potassium,  thus  the  potash  is  precipitated  and  lime 
salts  go  into  the  drainage  water ;  when  lime  is  applied 
to  the  land  the  process  is  reversed  and  potash  goes  into 
solution  as  bicarbonate. 

This  may  again  be  seen  in  the  results  quoted  in 
Table  LXXX.  of  the  application  of  lime  to  the 
Rothamsted  grass  plots :  on  Plot  8,  where  potash 
had  not  been  used  previous  to  the  application  of 
the  lime  there  is  little  or  no  increase  of  yield,  because 
there  were  no  reserves  of  potash  to  be  set  free.  That 
lime  acts  in  this  fashion  may  also  be  inferred  from 
its  beneficial  effect  upon  clovers  and  other  leguminous 
plants  in  a  mixed  herbage,  or  by  the  remarkable 
power  of  basic  slag  to  promote  the  growth  of  white 
clover  in  a  pasture  where  it  was  formerly  dormant 
Other  phosphatic  manures  have  often  little  effect  in 
such  cases,  so  that  free  lime  in  the  basic  slag,  by- 
liberating  potash,  is  evidently  as  important  a  factor  in 
the  growth  of  the  clover  as  the  phosphoric  acid.  If  the 
basic  slag  is  applied  to  a  soil  poor  in  potash  it  has 
little  effect,  and  again  after  two  or  three  applications 
to  grass  land  it  ceases  to  show  its  previous  beneficial 
action  upon  the  clover,  because  the  readily  attackable 
potash  in  the  soil  has  all  been  brought  into  solution 
and  a  direct  application  of  potash  salts  becomes 
necessary. 

The  fact  that  a  solution  of  calcium  bicarbonate  will 
react  with  the  potash-containing  double  silicates  in  the 
soil,  so  as  to  bring  some  of  the  potash  into  solution,  is 
only  a  particular  case  of  a  more  general  proposition, 
which  is  applicable  to  any  soluble  salt  brought  into 
contact  with  the  zeolites.  Whatever  the  salt  may  be, 
if  its  base  be  one  normally  found  in  the  zeolite,  e.g., 
either  sodium,  potassium,  calcium,  or  magnesium,  it  will 


262  MATERIALS  OF  INDIRECT  VALUE        [chap. 

effect  an  exchange  with  the  bases  in  the  zeoHte,  to  a 
greater  or  less  degree  according  to  the  relative  mass 
of  salt  and  zeolite,  becoming  itself  insoluble  and  bring- 
ing the  other  bases  into  solution.  Thus  in  practice  the 
application  of  any  soluble  salts  of  calcium,  magnesium, 
and  sodium  to  the  soil  results  in  potash  going  into 
solution  and  thus  becoming  available  for  the  crop, 
always  supposing  that  the  soil  is  provided  with  a 
normal  amount  of  clay  containing  zeolites  derived 
from  potash  felspar.  This  principle  serves  to  explain 
the  fertilising  value  of  all  such  bodies  as  gas  lime, 
gypsum,  salt,  and  sulphate  of  magnesia,  and  also  the 
irregularity  of  their  action,  because  they  are  only 
effective  when  the  soil  contains  potash  and  yet  the 
crop  requires  more  than  the  soil  can  normally  furnish. 

This  general  action  of  soluble  salts  in  increasing 
the  supply  of  available  potash  for  the  plant  may  be  well 
illustrated  from  the  Rothamsted  experiments.  Taking 
the  wheat  crop,  there  are  five  plots  treated  alike  as 
regards  their  supply  of  nitrogen  and  phosphoric  acid, 
but  whereas  one  receives  nothing  further,  one  each  of 
the  others  also  receives  sulphate  of  sodium,  potassium, 
or  magnesium  respectively,  and  the  fifth  plot  all  three 
of  these  salts,  with  the  results  set  out  in  Table  LXXXI. 
for  five  successive  ten-year  periods. 

It  will  be  seen  that  in  the  first  decade  the  lack  of 
any  alkaline  salt  on  Plot  1 1  caused  a  serious  reduction 
of  crop,  but  on  the  other  plots  there  was  much  the  same 
yield,  the  mixed  sulphates  giving  somewhat  the  highest 
and  the  sulphate  of  potash  itself  the  lowest  yield.  From 
this  alone  it  might  be  concluded  that  it  is  a  matter  of 
indifference  to  the  plant  which  of  the  alkaline  salts  it 
receives,  but  as  time  goes  on  it  will  be  seen  that  Plot 
13,  receiving  potash,  remains  but  little  behind  Plot  7 
receiving  all  the  salts,  but  that  Plots  12  and  14,  receiving 


IX.]       ACTION  OF  SOLUBLE  SALTS  UPON  SOIL      263 


soda  and  magnesia  without  potash,  fall  further  and 
further  behind,  though  they  never  reach  the  low  level 
of  Plot  II,  with  no  alkaline  salts  at  all.  At  first  the 
soda  and  magnesia  can  do  the  work  of  the  potash 
because  they  can  render  soluble  enough  potash  in  the 
soil  to  satisfy  the  needs  of  the  crop ;  but  as  the  treat- 

Table  LXXXI. — Effect  of  Alkaline  Salts  upon  the 
Wheat  Crop  (Rothamsted). 


l-H 

Alkaline  Salt  added  to 

ca 

Plot. 

Ammonium  Salts  and 

*-* 

•-; 

r-l 

r-t 

Superphosphate  in  Manure  :— 

S 

^ 

00 

Oi 

■^ 

r-l 

■^ 

•^ 

GRAIN, 

BUSHB 

LS. 

II 

None        .... 

28-4 

27-9 

21-7 

22-7 

19-5 

12 

Sulphate  of  Soda 

33-4 

34-3 

25-1 

30-1 

267 

13 

Sulphate  of  Potash   . 

32-9 

34-8 

26-8 

32-5 

29-6 

14 

Sulphate  of  Magnesia 

33-5 

34-4 

26-4 

3I-I 

2S-0 

7 

Sulphates  of  Soda,  Potash, 

and  Magnesia 

34-7 

35-9 

26-9 

35-0 

31-8 

STBAA 

V,  CWTS 

. 

II 

None        .... 

28-2 

24-5 

21-3 

20-8 

i8-8 

12 

Sulphate  of  Soda 

34-2 

30-5 

25-0 

27-3 

24-0 

13 

Sulphate  of  Potash    .         , 

34-4 

33-4 

27-6 

31-9 

28.6 

14 

Sulphate  of  Magnesia 

35-0 

30-7 

26-3 

28-6 

23.4 

7 

Sulphates  of  Soda,  Potash, 

and  Magnesia 

36-4 

34-3 

28.7 

34-1 

3I-I 

ment  is  continued  the  readily  attackable  potash  in  the 
soil  becomes  depleted  and  the  yield  falls  off  despite 
the  great  initial  store  of  potash  in  the  Kothamsted  soil. 
That  the  potash  in  the  soil  had  been  rendered  soluble  by 
the  soda  and  magnesia,  is  made  still  more  clear  by  a  con- 
sideration of  the  composition  of  the  ash  of  the  plants 
from  these  plots:  and  Table  LXXXII.  shows  the 
average  composition  of  the  straw  ash  for  the  10  years 


264 


MATERIALS  OF  INDIRECT  VALUE 


[chap. 


1882-91,  the  straw  ash  alone  being  given  because  there 
is  practically  no  variation  in  the  composition  of  the  ash 
of  the  grain. 

Table  LXXXIL— Percentage  Composition  of  the  Ash  of  Wheat 
Straw.  Mixed  Samples  representing  10  years,  1882-1891 
(Rothamsted). 


Ammonium  Salts  and  Superphosphate 

with — 

« 

<D      . 

rt  s 

0. 

^0 

3  Oj 

^j2 

mS 

m    =s 

Plot     . 

11 

12 

13 

14 

7 

Ash  (crude)  in  Dry  Matter, 

per  cent. 

5-84 

5-69 

5-93 

5-52 

5-89 

Iron  Peroxide,  etc.  , 

0-43 

0-33 

0-34 

0-41 

0-50 

Lime        .... 

9-14 

7-73 

5-39 

7-70 

5-69 

Magnesia         .        . 

2.25 

1-92 

1-53 

2-46 

1.76 

Potash     .... 

9-91 

14-68 

23-28 

14-87 

25-89 

Soda        .         .         •        . 

0-58 

0-57 

0.03 

0-33 

0-21 

Phosphoric  Acid       . 

4>26 

3-65 

3-39 

3-87 

3-82 

Sulphuric  Acid         . 

5-44 

5-33 

5-07 

5-31 

5-41 

Chlorine  .... 

1-66 

2-89 

5-6r 

2-81 

6.60 

Carbonic  Acid .         > 

trace 

none 

none 

trace 

Sihca        .... 

65.19 

61-93 

54.26 

6 1 -06 

49-68 

Sand        .... 

1-46 

1-43 

1-76 

1-39 

1-32 

Charcoal .         •        •        . 

Total     . 

o-o6 

0-19 

0-60 

0-42 

0-61 

100-38 

100-65 

101-26 

100-63 

101-49 

Deduct  0  =  QA. 
Total      . 

0-38 

0-65 

1-26 

0-63 

1.49 

1 00 -00 

lOO-OO 

loo-oo 

1 00 -00 

100-00 

There  is  no  great  variation  in  the  percentage  of  ash 
in  the  dry  matter,  but  while  the  percentage  of  potash  in 
the  ash  of  the  straw  from  Plot  13,  receiving  only  potash, 
is  23-28,  it  is  raised  to  25-89  when  soda  and  magnesia 


IX.]  GAS  LIME  265 

are  also  added  to  the  potash  in  the  manure,  but  sinks 
to  9-91  when  all  the  alkaline  salts  are  lacking.  From 
this  low  figure  of  9-91  the  addition  of  soda  causes  a 
rise  to  14-68,  of  magnesia  to  14-87 ;  the  differences  in 
the  yield  of  the  plots  are  in  fact  reflected  in  the  pro- 
portions of  potash  in  the  ash,  though  the  variations 
are  not  so  great.  But  though  the  addition  of  soda  or 
magnesia  on  Plots  12  and  14  causes  an  increase  in  the 
proportion  of  potash  in  the  ash,  neither  the  magnesia 
nor  the  soda  in  the  ash  are  perceptibly  raised.  Hence, 
we  may  conclude  that  the  whole  effect  of  either  sulphate 
of  soda  or  sulphate  of  magnesia  upon  the  crop  is 
indirect  and  due  to  their  attack  upon  the  potash 
reserves  in  the  soil. 

These  results  with  wheat  at  Rothamsted  are  con- 
firmed by  the  parallel  experiments  upon  mangolds  and 
grass ;  in  each  case  sodium  and  magnesium  salts  add  to 
the  effect  of  a  potash  dressing,  and  in  the  absence  of 
potash  partially  do  its  work,  more  in  the  earlier  than  in 
later  years  of  the  experiment  when  the  easily  attacked 
soil  potash  is  becoming  exhausted. 

Gas  lime  is  a  greenish  yellow,  evil  smelling  sub- 
stance obtained  during  the  purification  of  coal-gas  by 
its  passage  over  trays  of  freshly  slaked  lime,  which 
absorbs  sulphuretted  hydrogen  and  other  sulphur  com- 
pounds from  the  crude  gas.  Various  sulphides  and 
partially  oxidised  sulphur  compounds  of  calcium  are 
formed,  as  may  be  seen  from  the  analyses  set  out  below, 
and  these  are  to  some  extent  attacked  by  the  carbon 
dioxide  of  the  air  with  the  liberation  of  the  original 
gaseous  sulphur  compounds.  The  main  action,  however, 
on  exposure  to  the  air  is  one  of  oxidation,  so  that 
eventually  the  material  becomes  little  more  than  a 
mixture  of  gypsum  and  calcium  carbonate  from  the 
uncombined   lime.     It  is   in   this   oxidised  form   only 


266 


MATERIALS  OF  INDIRECT  VALUE 


[chap. 


that  gas  lime  should  be  appHed  to  the  land  unless  the 
ground  is  badly  infested  with  some  insect  pest  which 
the  raw  sulphur  compounds  may  check  or  destroy,  and 
even  then  on  light  soils  the  fertility  of  the  land  may  be 
impaired  for  some  time.  It  is  on  heavy  land  that  gas 
lime  is  of  most  value ;  the  flocculating  effect  of  the 
calcium  salts  improves  the  texture,  and  the  soil  also 
contains  a  great  reserve  of  dormant  potash  compounds 
to  be  rendered  soluble.  The  crude  material  from  the 
gas  works  should  be  laid  up  in  heaps,  mixed  with  a 
little  earth  for  a  year  or  more,  spread  on  the  stubbles  in 
the  early  autumn,  and  then  ploughed  in. 

Table  LXXXIII. — Analyses  of  Gas  Lime. 


London, 
fresh. 

London, 

a  little 

Oxidised. 

Oxidised. 

Water 

19-2 

32-3 

30-1 

Calcium  Hydrate  (Slaked  Lime) 

I5-I 

17-7 

32-6 

„        Carbonate 

24-2 

44-5 

17-5 

„        Sulphide 

6.9 

trace 

„        Thio-sulphate 

11-8 

12-3 

„        Oxy-sulphide 

3-2 

„        Sulphite 

1-5 

14-57 

\     20-2 

„        Sulphate 

0-25 

2-80 

Sulphur 

4-3 

5-14 

Silica,  etc 

3-55 

0-71 

... 

Gypsum. — That  gypsum,  crystallised  sulphate  of 
lime,  or  land  plaster,  CaSO^,  2H2O,  had  a  beneficial 
effect  upon  certain  crops  and  soils  has  been  known  for 
a  very  long  time ;  it  was  probably  familiar  to  the 
Romans,  and  the  knowledge  survived  to  a  certain 
degree  among  the  southern  nations,  especially  in  con- 
nection with  vines.  In  Britain  it  appears  to  have  been 
less  commonly  used  and  no  very  general  agreement  as 
to  its  value  had  become  traditional ;  in  fact  it  was  only 
among  the  hop  growers  of  Kent  and  especially  of  Sussex, 


IX.]  GYPSUM  267 

that  any  regular  use  was  made  of  gypsum.  In  this 
latter  case  it  is  not  easy  to  make  out  to  what  extent  its 
employment  was  the  result  of  experience,  or  of  a  quasi- 
scientific  opinion  which  traced  a  connection  between  the 
action  of  sulphur  upon  the  mildew  of  the  hop,  a 
supposed  lack  of  sulphates  in  a  mildewed  leaf,  and 
the  sulphates  in  the  gypsum.  In  the  latter  part  of 
the  eighteenth  century  the  value  of  gypsum  for  legu- 
minous crops  like  clover  and  lucerne  became  widely 
recognised ;  Benjamin  Franklin,  in  America,  is  said  to 
have  sown  gypsum  so  as  to  form  the  word  "plaster"  on 
clover  crops  by  the  wayside,  in  order  that  passers  by 
should  learn  by  the  eye  what  had  so  stimulated  the 
growth.  It  is,  in  fact,  on  leguminous  and  such  other 
crops  as  are  specially  dependent  upon  potash,  that 
gypsum  has  an  effect.  This  is  intelligible  on  the 
principle  set  out  above,  that  the  solution  of  calcium 
sulphate  which  arises  from  the  gypsum  will  attack  the 
zeolites  containing  potash  and  will  so  bring  some 
potassium  sulphate  into  solution  in  the  soil  water. 
In  confirmation  of  this  view,  Boussingault  has  shown 
that  when  clover  is  manured  with  gypsum  and  improved 
thereby,  the  ash  of  the  crop  contains  a  greater  pro- 
portion of  potash  but  shows  no  increase  in  either  the 
lime  or  the  sulphuric  acid. 

The  figures  obtained  by  Boussingault  are  set  out  in 
Table  LXXXIV. 

Thus,  while  the  variations  in  lime  and  sulphuric 
acid — the  constituents  of  the  gypsum,  are  small,  the 
proportion  of  potash  has  been  greatly  increased  by  the 
use  of  gypsum. 

Similarly,  it  has  been  found,  in  testing  the  action  of 
gypsum  upon  hops,  that  it  has  a  beneficial  effect  only 
upon  the  soils  where  hops  also  respond  to  dressings  of 
potash   salts,  and   that   the   result    of    applications  of 


268 


MATERIALS  OF  INDIRECT  VALUE 


[chap. 


gypsum  is  similar  to  that  of  potash  salts,  though  to  a 
less  degree.  Some  crops,  like  Swede  turnips  and 
cabbage,  may  take  up  more  sulphur  compounds  than 
the  soil  can  normally  supply  and  so  be  benefited  by  the 
sulphur  in  the  gypsum,  but  in  the  main  its  value  is  as  a 
liberator  of  potash  in  the  soil. 

Table  LXXXIV.— Composition  of  Clover  Ash. 


Potash 

Soda  ..... 

Magnesia  ..... 
Lime  ..... 

Oxides  of  Iron  and  Manganese  . 
Chlorine   .         .         .         .         . 
Phosphoric  Acid 
Sulphuric  Acid .... 
Silica        .         .         ,         .         . 


Without 
Gypsum. 


23-6 
I -2 
7-6 

28-5 

1-2 

4-1 
9-7 

3-9 

20'0 


With 
Gypsum. 


35-4 
0-9 

6-7 
39-4 
i-o 
3-8 
9-0 

3-4 
iO'4 


Salt. — The  use  of  salt,  alone  or  as  an  adjunct  to 
other  fertilisers,  is  a  common  farming  practice ;  for 
example,  in  growing  mangolds  it  is  customary  to  give 
them  2  or  3  cwt.  per  acre  of  salt  as  a  top  dressing  with 
or  without  nitrate  of  soda.  On  the  fen  land  of  Lincoln- 
shire potatoes  are  generally  grown  with  farmyard 
manure,  superphosphate,  and  a  liberal  dressing  of  salt, 
and  in  barley  growing,  salt  alone  is  sometimes  used 
where  roots  have  been  folded  off,  with  an  idea  of 
stiffening  the  straw.  Though,  in  the  first  case,  the  value 
of  salt  is  often  ascribed  to  the  fact  that  the  mangold 
has  been  derived  from  a  maritime  plant,  it  is  really 
due  to  the  dependence  of  mangolds  upon  an  abundant 
supply  of  potash  (see  p.  i68),  because  the  soluble 
sodium  chloride  will  bring  into  solution  the  reserves  of 
insoluble  potash  in  the  soil  and  the  manure.  Potatoes 
again   are   much   in    need    of    potash,   and    the   straw 


IX.]  SALT  269 

stiffening  effect  is  similarly  explicable  by  the  extra 
potash  made  available  for  the  barley  plant.  Even  the 
ill  effects  of  salt  upon  the  malting  quality  of  the  barley 
that  are  sometimes  experienced,  can  be  paralleled  by 
the  observed  effects  of  potash  in  prolonging  the  growth 
of  barley  and  deepening  the  colour  of  the  grain.  Salt 
is  also  credited  at  times  with  injuring  the  tilth  of  heavy 
soils  and  rendering  them  sticky  and  wet ;  this  effect 
again  is  paralleled  by  the  action  of  potash  salts  (p.  176) ; 
an  interaction  takes  place  between  the  salt  and  the 
carbonate  of  lime  in  the  soil,  and  a  little  free  alkaline 
carbonate  is  formed,  which  deflocculates  the  clay. 

We  may  therefore  conclude  that  the  action  of  salt 
is  entirely  indirect,  rendering  available  the  potash  in  the 
soil  instead  of  itself  feeding  the  crop.  None  the  less  it 
forms  a  valuable  adjunct  to  other  manures  for  all  crops 
requiring  large  supplies  of  potash,  such  as  mangolds  and 
other  root  crops,  and  may  greatly  economise  if  not 
entirely  replace  the  use  of  potash  salts  themselves.  In 
some  districts  a  waste  product  termed  "  gunpowder 
salt "  is  obtainable ;  this  is  the  bye-product  in  the 
manufacture  of  saltpetre  by  the  interaction  of  nitrate  of 
soda  and  potassium  chloride,  and  is  identical  with 
common  salt  except  that  it  also  contains  a  little  nitrate 
and  some  potash.  These  technical  impurities  render  it 
more  valuable  for  agricultural  purposes,  so  that  it  forms 
a  very  excellent  top  dressing  for  mangolds. 

Sulphate  of  Magnesia. — The  action  of  this  salt  has 
already  been  explained  (p.  262) ;  it  is  never  required  to 
supply  the  plant  with  magnesia,  sufficient  quantities  of 
which  are  to  be  found  in  all  ordinary  soils  for  the  needs 
of  the  crop,  and  while  it  would  render  available  some 
potash  in  the  soil,  common  salt  will  do  the  same  thing 
more  cheaply.  Carbonate  of  magnesia  has  from  time 
to  time  been  suggested,  and  even  put  upon  the  market, 


270  MATERIALS  OF  INDIRECT  VALUE        [chap. 

as  a  manure,  but  there  is  no  evidence  to  show  that  its 
action  is  in  any  way  different  from  that  of  calcium 
carbonate,  i.e.^  it  behaves  as  a  base  but  is  not  of  any 
further  value  as  supplying  magnesia  to  the  plant. 

Sulphate  of  Iron. — It  is  well  known  that  iron  is  one 
of  the  essential  constituents  of  all  green  plants ;  for 
example,  in  water  cultures  it  is  easy  to  show  that 
seedling  plants  become  blanched,  chlorophyll  does  not 
form  in  the  leaf,  and  the  plants  soon  die,  unless  a 
small  quantity  of  some  soluble  iron  compound  is 
added  to  the  culture  liquid.  Such  an  addition  is 
followed  by  a  rapid  return  of  the  green  colour  to  the 
leaf  and  by  the  renewed  growth  of  the  plant.  A 
very  widespread  opinion  has  been  based  upon  such 
experiments  and  is  specially  current  in  horticultural 
literature,  that  high  colour  in  fruit  and  flowers 
is  to  be  associated  with  an  abundance  of  iron  com- 
pounds in  the  soil,  and  that  in  consequence  sulphate  of 
iron  is  valuable  as  an  adjunct  to  manures.  One  argu- 
ment advanced  in  favour  of  this  opinion  is  the  bright 
colouring  of  apples,  roses,  etc.,  grown  on  the  red  sand- 
stones and  loams  of  Herefordshire  and  Worcestershire, 
the  red  hue  of  which  is  admittedly  due  to  oxides  of  iron. 
When  the  facts  are  more  closely  examined,  they  afford, 
however,  little  support  to  such  a  theory.  In  the  first 
place,  the  plant  requires  very  little  iron  indeed :  as  a 
rule,  not  more  than  i  per  cent,  of  the  ash  of  a  plant 
consists  of  oxide  of  iron,  2  per  cent,  might  be  taken  as 
an  outside  limit,  so  that  the  amount  of  oxide  of  iron 
taken  from  the  soil  by  a  heavy  crop  of  mangolds  (the 
leaf  of  which  is  specially  rich  in  iron)  only  amounts  to 
about  10  lbs.  per  acre.  Now  it  is  very  rare  to  meet 
with  a  soil  that  does  not  contain  2  per  cent,  (or  20  tons 
per  acre  in  the  top  9  inches)  of  oxide  of  iron  soluble  in 
hydrochloric  acid,  and  of  this  a  considerable  proportion 


IX.]  FUNCTION  OF  IRON  SALTS  271 

is  soluble  in  the  weakest  acids  and  must  be  regarded  as 
available  for  the  plant.  Moreover,  the  red  sands  and 
loams  mentioned  above  show  rather  less  than  the  normal 
amount  of  iron  on  analysis  ;  the  bright  red  colour  is 
due  to  some  variation  in  the  mode  of  deposition  of  the 
oxides  of  iron  and  not  to  any  excess  in  their  amount. 
These  facts  alone  render  the  theory  improbable,  but  the 
chief  point  is  that  no  direct  evidence  has  been  adduced 
for  the  beneficial  effect  of  an  application  of  iron  salts, 
either  on  colour  or  yield.  From  time  to  time  experi- 
ments with  iron  sulphate  have  been  quoted,  but  they  have 
never  been  conducted  in  a  manner  to  raise  the  supposed 
increase  due  to  the  iron  beyond  the  range  of  experi- 
mental error.  Even  had  the  results  been  positive  they 
would  have  required  futher  examination,  because  the 
application  of  sulphate  of  iron  to  the  soil  would  result 
in  a  variety  of  secondary  effects,  due  to  the  precipitation 
of  the  iron  and  the  solution  of  a  corresponding  amount 
of  other  bases  present.  As  far  as  colour  goes,  no 
evidence  has  ever  been  adduced  to  show  that  iron  plays 
a  part ;  experiments  made  by  the  author  upon  apples 
gave  purely  negative  results ;  and  though  some  effects 
upon  the  colour  of  carnations  were  seen,  no  positive 
conclusions  could  be  drawn.  In  practice  the  employ- 
ment of  sulphate  of  iron  for  either  farm  or  garden 
crops  may  be  dismissed. 

Manganese  appears  also  to  be  a  constituent  of  all 
plants,  and  recently  experiments  have  been  put  forward 
to  show  that  small  quantities  of  manganese  salts  have 
a  stimulating  effect  upon  the  growth  of  crops.  The 
experiments  are,  however,  by  no  means  conclusive,  and 
pending  further  investigations,  the  use  of  manganese 
salts  cannot  be  recommended  in  practice. 

Silicates, — Silica  is  so  large  a  constituent  of  the  ash 
of  many  plants,  particularly  of  the  straw  of  cereals,  that 


272  MATERIALS  OF  INDIRECT  VALUE        [chap. 

it  was  inevitably  regarded  as  a  necessary  constituent  of 
the  food  of  such  plants,  and  was  naturally  enough 
supposed  to  contribute  to  the  stiffness  of  the  straw. 
In  his  manures  Liebig  supplied  the  alkalies  combined 
with  silica,  and  when  Way  discovered  that  certain 
strata  of  the  Upper  Greensand,  near  Farnham,  con- 
tained considerable  quantities  of  silicates  readily  dis- 
solved by  acids,  the  rock  was  for  a  time  extracted 
and  ground  up  as  a  manure  for  cereals.  But  Sachs 
showed  that  these  plants,  however  rich  in  silica 
their  ash  was  when  they  had  grown  on  ordinary  soil, 
could  yet  be  grown  with  complete  success  in  a  water 
culture  devoid  of  any  silica,  and  Jodin  succeeded  even 
in  raising  four  generations  of  maize  in  water  cultures 
with  no  more  silica  than  was  contained  in  the  original 
seed.  It  was  also  shown  that  the  stiffness  of  the  straw 
depended  upon  such  physiological  factors  as  light  and 
exposure,  rapidity  of  growth,  etc.,  and  was  independent 
of  the  amount  of  silica  present,  so  that  the  use  of 
silicates  for  manurial  purposes  ceased,  except  at  the 
instance  of  one  or  two  unscrupulous  firms  puffing 
worthless  materials.  However,  it  must  not  be  supposed 
that  so  large  a  constituent  of  a  plant's  ash  is  entirely 
without  physiological  function,  and  from  the  Rothamsted 
barley  experiments  (which  include  plots  receiving 
sodium  silicate)  it  may  be  seen  that  soluble  silica  does 
play  some  part,  at  present  not  properly  understood, 
which  enables  the  plant  to  make  better  use  of  the 
dormant  phosphoric  acid  in  the  soil.  The  silicates, 
however,  possess  no  practical  use  as  fertilisers,  the 
increase  thus  produced  would  not  repay  the  expense 
of  applying  the  silicate  of  soda. 

Green  manuring. — Green  manuring  consists  in  the 
ploughing  under  of  some  rapidly  growing  crop — mustard 
or  tares  in  this  country,  lupins  on  sandy  soils  on  the 


IX.]  GREEN  MANURES  273 

Continent,  and  covvpeas  in  America  being  among  the 
plants  most  commonly  employed.  The  practice  has 
three  objects : — 

(i)  The  improvement  of  the  texture  of  the  land  by 
increasing  the  store  of  humus ;  this  is  particularly 
valuable  on  heavy  clays  and  on  the  light  sandy  soils 
at  the  other  end  of  the  scale. 

(2)  The  saving  of  the  store  of  nitrates,  which  on 
light  warm  soils  form  with  great  rapidity  after  harvest, 
and  which  may  then  easily  be  washed  away.  If  some 
catch  crop  like  mustard  is  sown  immediately  the  stubbles 
are  clear,  it  will  grow  with  great  rapidity  after  the  first 
rain  and  will  gather  up  these  nitrates,  converting  them 
into  proteins,  which  become  more  slowly  available  on 
the  decay  of  the  plant  material. 

(3)  For  cleaning  purposes ;  when  the  land  is  in  very 
foul  condition  a  good  many  weeds  can  be  got  rid  of  by 
growing  a  smothering  crop. 

On  many  soils  green  manuring  may  be  extremely 
valuable,  especially  where  there  is  any  shortage  of 
farmyard  manure ;  a  green  crop  of  mustard  turned  in, 
especially  if  it  had  been  previously  manured  with  some 
mixture  of  artificials,  will  have  all  the  lasting  beneficial 
effects  of  a  coat  of  dung.  Of  course  the  "  seeds  "  crop 
in  the  rotation  has  much  the  same  effect,  because  of  the 
roots  and  stubble  left  behind,  but  it  does  not  always 
come  round  often  enough  in  the  rotation  to  keep  the 
land  in  condition. 

When  vetches,  lupins,  or  other  leguminous  crops  are 
grown,  the  land  is  also  enriched  by  the  nitrogen  gathered 
from  the  atmosphere  by  the  bacteria  living  in  the  root 
nodules,  and  large  areas  of  land  in  Pomerania  and  East 
Prussia  have  been  brought  under  cultivation  from  the 
state  of  barren  sandy  heath,  by  ploughing   in   lupins 

S 


274  MATERIALS  OF  INDIRECT  VALUE        [chap. 

manured  with  basic  slag  and  potash  salts,  until  a  soil 
had  been  built  up. 

Curiously  enough,  on  the  sandy  soil  at  Woburn, 
Voelcker  has  always  obtained  better  crops  after  mustard 
than  after  vetches,  despite  the  fact  that  the  vetches  had 
contributed  a  greater  weight  both  of  dry  matter  and 
nitrogen  to  the  land.  The  vetch  compounds  may  decay 
the  more  slowly,  but  Voelcker  further  showed  that  the 
land  was  left  drier  by  the  vetch  crop ;  that  this  was 
the  cause  of  the  superiority  of  the  mustard  as  a 
green  manure  is  rendered  more  probable  by  the  fact 
that  the  result  was  reversed  on  the  strong  Rothamsted 
soil,  where  the  vetches  are  the  better  preparation  for  a 
succeeding  wheat  crop.  The  real  difficulty  experi- 
enced in  utilising  green  manuring  and  catch  crops 
generally  on  many  soils  in  this  country,  to  which  they 
are  otherwise  most  admirably  suited,  is  the  way  they 
deplete  the  water-supply  for  the  succeeding  crop.  For 
example,  a  crop  of  vetches  or  crimson  clover  may  be 
sown  on  the  stubble  in  August  or  September  and 
harvested  in  May,  in  plenty  of  time  to  prepare  the  land 
for  turnips,  but  in  many  cases  the  soil  and  subsoil  will 
be  left  so  dry  that  the  turnip  crop  will  fail  or  be  greatly 
reduced,  unless  the  incidence  of  rain  be  unusually 
favourable.  The  difficulty  of  starting  the  catch  crop 
after  the  drying  effect  of  the  harvested  corn,  and  the 
dryness  of  the  land  which  again  ensues  after  the 
catch  crop  in  spring,  form  the  great  objection  to  catch- 
cropping,  which  indeed  only  flourishes  where  the  annual 
rainfall  is  well  over  30  inches.  In  this  respect  mustard 
is  the  least  objectionable  crop,  since  it  will  grow  in 
six  or  eight  weeks  under  good  conditions  in  autumn, 
and  can  then  be  turned  in,  leaving  the  ground  broken 
to  catch  the  late  winter  rainfall.  On  the  light  soils 
it  is  more  general  to  fold  sheep   on  the  catch  crops 


IX.]  CATCH  CROPS  275 

than  to  plough  them  in,  and  though  the  greater  part  of 
the  humus  is  thus  lost  to  the  land,  there  is  still  a  con- 
siderable gain,  while  the  essential  manurial  substances — 
nitrogen,  phosphoric  acid,  and  potash — are  almost 
wholly  returned  to  the  soil.  Where  the  land  is  light 
enough  to  be  improved  by  the  treading  of  sheep  and 
the  rainfall  admits  of  catch-cropping,  there  is  no  better 
way  of  building  up  a  fertile  soil  than  by  folding ;  the 
actual  enrichment  of  the  soil  can  be  effected  either  by 
manuring  for  the  catch  crops  with  inorganic  fertilisers 
like  superphosphate  and  nitrate  of  soda  or  by  consuming 
cake  and  corn  with  them.  The  losses  inherent  in  making 
dung  are  thus  obviated,  for  when  the  urine  falls  directly 
on  the  land,  no  evaporation  of  ammonia  is  allowed  to 
take  place  ;  no  labour  is  required  ;  the  tilth  of  the  land 
is  improved  by  the  humus  and  the  trampling  of  the 
sheep ;  no  more  effective  nor  cheaper  system  of  growing 
corn  can  be  devised  than  to  alternate  it  with  green  crops 
consumed  on  the  land,  as  is  practised  with  so  much 
success  on  the  brick  earths  of  West  Sussex  and  the 
chalky  loams  of  Wiltshire. 


CHAPTER   X 

THEORIES   OF   FERTILISER   ACTION 

Liebig's  Ash  Theory — Part  played  by  the  Soil  in  the  Nutrition  of 
the  Crop — Villa's  Theory  of  Dominants — Liebig's  Law  of  the 
Minimum — Law  of  diminishing  Returns — Limiting  Factors 
in  Plant  Growth — Is  the  Composition  of  the  Soil  Water 
unaffected  by  Fertilisers  ? — Attack  of  the  Plant's  Roots  upon 
Insoluble  Fertilisers — The  Part  played  by  Carbon  Dioxide  in 
the  Soil — Excretion  of  Toxic  Substances  from  Plant  Roots — 
Rotations  as  a  Substitute  for  Fertilisers — Unexplained  Factors 
in  the  Nutrition  Problem. 

It  is  to  Liebi'g  that  we  owe  the  first  general  theory  of 
the  nutrition  of  the  plant  and  the  function  of  fertilisers  : 
although  Liebig  himself  did  not  add  anything  to  the 
knowledge  of  the  process  of  carbon  assimilation  which 
had  been  acquired  by  Priestley,  Senebier,  and  others, 
nor  to  the  study  of  the  nitrogen  and  ash  constituents 
which  had  been  begun  by  de  Saussure,  he  yet  drew  up 
from  these  facts  a  coherent  theory  of  the  course  of 
nutrition,  and  put  it  before  the  world  with  such  vivid- 
ness that  it  forthwith  took  its  place  in  the  general  body 
of  accepted  scientific  opinion.  Liebig  argued  that  since 
the  ash  constituents  alone  are  drawn  from  the  soil,  it 
is  only  necessary  that  there  shall  be  no  deficiency  in 
such  inorganic  materials  as  are  left  behind  when  the 
plant  is  burnt,  in  order  to  ensure  the  complete  nutrition 
of  the  plant.     According  to  Liebig,  the  function  of  the 

2T6 


CHAP.  X.]  LIEBIG'S  THEOR  Y  OF  PLANT  NUTRITION  277 

fertiliser  is  to  supply  to  the  soil  the  materials  removed 
therefrom  by  the  crop,  and  the  fertiliser  required  can 
be  ascertained  beforehand  by  the  analysis  of  a  similar 
crop,  so  that  the  soil  can  be  supplied  with  the  exact 
amounts  of  potash,  soda,  magnesia,  lime,  phosphoric 
acid,  etc.,  which  would  be  removed  by  a  normal  yield 
of  that  particular  crop.  Neglecting  Liebig's  miscon- 
ception of  the  source  of  the  plant's  nitrogen  and  the 
long  controversy  which  arose  as  to  the  necessity  of  its 
artificial  supply,  we  can  restate  the  theory  as  assuming 
that  the  proper  fertiliser  for  any  particular  crop  must 
contain  the  amounts  of  nitrogen,  phosphoric  acid,  potash, 
and  other  constituents  which  are  withdrawn  from  the 
soil  by  a  typical  good  yield  of  the  plant  in  question. 

In  this  form  the  opinion  that  the  composition  of  the 
crop  affords  the  necessary  guide  to  its  manuring  pre- 
vailed for  some  time  and  still  survives  in  horticultural 
publications,  but  the  course  of  field  experiments, 
particularly  those  at  Rothamsted,  and  the  accumula- 
tion of  farming  experience  soon  demonstrated  that  it 
was  a  very  imperfect  approximation  to  the  truth. 
Liebig's  theory  fails  because  it  takes  no  account  of  the 
soil  and  of  the  enormous  accumulation  of  plant  food 
therein  contained.  Water  culture  experiments  demon- 
strated that  certain  elements,  e.g.,  sodium  and  silica, 
though  universally  present  in  the  plant's  ash,  are 
unessential  to  its  nutrition.  Field  experiments  also 
showed  that  other  elements  —  magnesium,  calcium, 
chlorine,  sulphur,  iron — though  essential,  are  always 
supplied  in  sufficient  quantities  by  all  normal  soils. 
Thus  the  elements  to  be  supplied  by  the  fertiliser 
became  reduced  to  three — nitrogen,  phosphorus,  and 
potassium — and  even  the  amounts  required  of  each  of 
these  are  not  indicated  by  the  composition  of  the  crop. 
To  take  an  example — normal  crops  of  barley  and  wheat 


278 


THEORIES  OF  FERTILISER  ACTION       [chap. 


would  withdraw  from  the  soil  approximately  the  follow 
ing  fertilising  materials. 

Table  LXXXV.— Fertilising  Constituents  contained 
IN  Wheat  and  Barley  Crops. 


Yield 
of  Grain, 

Bushels. 

Lb.  per  acre  Removed. 

Nitrogen. 

Phosphoric 
Acid. 

Potash. 

Wheat 
Barley          , 

36 
48 

50 
49 

21 
21 

29 
36 

Now  the  results  of  field -experiments,  which  are 
abundantly  confirmed  by  ordinary  farming  experience, 
go  to  show  that  the  yield  of  wheat  is  chiefly  determined 
by  the  supply  of  nitrogen ;  phosphoric  acid  is  of  second- 
ary importance,  and  only  on  exceptional  soils  will  there 
be  any  return  for  the  application  of  potash.  With 
barley,  though  its  composition  is  very  similar  to  that 
of  wheat,  the  results  are  very  different :  nitrogen  is  still 
the  most  important  element  in  nutrition,  but  phosphoric 
acid  has  equally  marked  effects,  whilst  in  ordinary  soils 
potash  counts  for  little  or  nothing. 

This  may  be  illustrated  from  the  Rothamsted  experi- 
ments, and  the  part  played  by  the  reserves  in  the  soil 
will  be  made  evident  by  comparing  the  results  obtained 
in  the  first  and  the  fifth  series  of  ten  years. 

The  analysis  of  the  barley  plant  would  indicate  that 
it  requires  nitrogen  in  the  largest  amounts,  then  potash, 
and,  least  of  all,  phosphoric  acid ;  but  if  the  results  for 
the  first  ten  years  of  the  experiment  are  considered,  it 
will  be  seen  that  the  omission  of  either  nitrogen  or 
phosphoric  acid  from  the  fertiliser  causes  a  big  decline 
in  yield  in  comparison  with  that  of  the  completely 
fertilised  plot.  The  omission  of  potash,  however,  is  of 
little  or  no  moment,  since  it  only  causes  the  yield  to  fall 


X.] 


FERTILISERS  REQUIRED  BY  BARLEY 


279 


from  46-1  to  45-6  bushels  per  acre.  Evidently  the  soil 
was  able  to  supply  all  the  requirements  of  the  plant  for 
potash,  despite  the  large  amounts  which  the  crop 
removes.  In  the  latter  years  of  the  experiment  this 
stock  of  available  potash  in  the  soil  had  become  some- 
what depleted,  so  that  the  omission  of  potash  from  the 
fertiliser  reduced  the  yield  from  36-3  to  28-0  bushels  per 
acre.    The  exhausted  soil  in  these  latter  years  causes  the 

Table  LXXXVI. — Average  Yield  of  Barley  Grain  (Hoos 
Field,  Rothamsted). 


Plot. 


Manuring. 


Average  Yield  of  Grain, 
Bushels. 

First 

Fifth 

10  years 
(1852-1861). 

10  years 
(1892-1001). 

46-1 

36-3 

35-0 

22-1 

45-6 
33-6 

28-0 

i6-6 

30-5 

12-8 

22-4 

lo-o 

4A 

3A 

2A 

lA 
4O 

lO 


Complete  Fertiliser — Nitrogen,  Phosphoric 

Acid,  Potash 

Phosphoric   Acid   omitted — Nitrogen   and 

Potash 

Potash  omitted — Nitrogen  and  Phosphoric 

Acid 

Nitrogen  only    ...... 

Nitrogen   omitted — Phosphoric  Acid    and 

Potash 

Unmanured        ...... 


crop  to  respond  to  the  constituents  of  the  fertiliser  only 
when  they  are  all  present  together ;  taken  singly,  they 
increase  the  yield  but  little,  and  the  omission  of  any  one 
of  them  reduces  the  crop  almost  to  the  minimum  pro- 
duced on  the  unmanured  plot.  The  soil  has  thus  become 
but  a  small  factor  in  the  nutrition  of  the  crop,  whereas, 
as  regards  potash,  it  was  a  very  large  one  at  the  begin- 
ning of  the  experiment,  and  the  defect  of  Liebig's  theory 
was  to  neglect  it  entirely. 

These  differences  in  the  manurial  requirements  of 
wheat    and    barley,   differences   which   would    not    be 


28o  THEORIES  OF  FERTILISER  ACTION       [chap. 

apprehended  from  their  respective  compositions,  may 
be  correlated  with  the  habits  of  growth  of  the  two 
plants :  wheat  is  sown  in  the  autumn  after  but  a  slight 
preparation  of  the  ground,  nitrification  is  thus  restricted, 
especially  as  the  chief  development  of  the  plant  takes 
place  in  the  winter  and  early  spring  before  the  soil  has 
warmed  up ;  as  a  consequence,  the  crop  is  particularly 
responsive  to  an  external  supply  of  some  active  form  of 
nitrogen.  On  the  other  hand,  the  wheat  plant  possesses 
a  very  extensive  root  system  and  a  long  period  of 
growth,  hence  it  is  specially  well  fitted  to  obtain 
whatever  mineral  constituents  may  be  available  in  the 
soil.  In  ordinary  farming  the  only  fertiliser  used  for 
the  wheat  crop  will  be  a  spring  top-dressing  of  i  cwt. 
per  acre  or  so  of  nitrate  of  soda,  or  an  equivalent 
amount  of  sulphate  of  ammonia  or  soot. 

Barley  is  a  spring-sown  crop,  for  which  the  soil 
generally  receives  a  more  thorough  cultivation ;  in 
consequence  the  nitrates  produced  with  the  rising 
temperature  will  be  sufficient  for  the  needs  of  the 
crop ;  often  more  than  enough  when  the  barley  follows 
a  root  crop  that  has  been  liberally  manured  and  perhaps 
consumed  on  the  ground  by  sheep.  But  being  shallow- 
rooted,  and  having  only  a  short  growing  season,  the 
barley  plant  experiences  a  difficulty  in  satisfying  its 
requirements  for  phosphoric  acid,  hence  the  necessary 
fertiliser  consists,  in  the  main,  of  this  constituent.  Only 
on  sandy  and  gravelly  soils,  exceptionally  deficient  in 
potash  and  subject  to  drought,  is  any  benefit  derived 
from  a  supply  of  potash  to  the  barley  crop. 

A  still  more  noteworthy  example  is  provided  by  the 
Swede  turnip  crop ;  an  analysis  of  a  representative 
yield  would  show  it  to  withdraw  from  the  soil  about 
150  lb.  per  acre  of  nitrogen,  30  lb.  of  phosphoric  acid, 
and  120  lb.  of  potash.     Yet  the  ordinary  fertiliser  for 


X.]  DOMINANT  MANURES  281 

the  Swede  crop  will  consist  in  the  main  of  phosphatic 
material,  with  but  a  small  quantity  of  nitrogen  and 
rarely  or  never  any  potash.  For  example,  4  cwts.  of 
superphosphate  or  5  cwts.  of  basic  slag,  according  to 
the  soil  {i.e.,  50  to  100  lb.  of  phosphoric  acid),  together 
with  12  to  15  lb.  of  nitrogen  as  contained  in  half  a 
hundredweight  of  sulphate  of  ammonia,  will  form  a 
very  satisfactory  mixture.  Swedes  are  sown  late  in 
the  season  after  a  very  thorough  preparation  of  the  soil, 
so  that  the  nitrification  alone  of  the  nitrogenous  residues 
in  the  soil  is  capable  of  furnishing  almost  all  the  large 
amount  of  nitrogen  they  require  ;  they  are  very  shallow- 
rooted,  and  must  be  supplied  with  an  abundance  of 
phosphoric  acid.  It  was  considerations  of  this  kind 
which  led  Ville  to  suggest  that  for  each  crop  there  is  a 
"  dominant "  fertilising  constituent,  e.g.,  nitrogen  for 
wheat,  phosphoric  acid  for  Swedes,  and  that  the  parti- 
cular dominant  is  the  constituent  which  the  plant  finds 
the  most  difficulty  in  appropriating  from  the  soil,  and 
which  is,  therefore,  more  often  indicated  by  a  compara- 
tive deficiency  than  by  an  abundance  in  the  ash  of  the 
plant.  Such  a  theory  is,  however,  not  borne  out  by  more 
general  experiments ;  many  plants  do  not  exhibit  such 
idiosyncrasies  as  are  shown  by  wheat  and  Swedes,  but 
require  a  general  fertiliser,  the  composition  of  which  is 
determined  more  by  the  soil  than  the  plant.  Indeed,  no 
theory  of  manuring  can  be  based  upon  the  plant  alone 
but  must  also  take  the  soil  into  account,  so  that  a 
fertiliser  may  be  regarded  as  rectifying  the  deficiencies 
of  the  soil  as  far  as  regards  the  requirements  of  the  crop 
in  question.  What  those  special  requirements  are  can 
only  be  decided  by  experiment,  just  as  the  soil  con- 
ditions are  ascertainable  by  trial  rather  than  from  a 
priori  considerations  of  analysis.  If  an  analysis  be 
made   of  any  soil  in   cultivation   it   will   be  found   to 


282  THEVRIES  OF  FERTILISER  ACTION       [chap. 

contain  sufficient  plant  food  for  the  nutriment  of  a 
hundred  or  more  full  crops :  the  soil  of  the  unmanured 
plot  on  the  Rothamsted  wheatfield  contained  in  1893, 
after  fifty-four  years'  cropping  without  fertiliser,  2570  lb. 
per  acre  of  nitrogen,  2950  lb.  of  phosphoric  acid,  and 
5700  lb.  of  potash.  Of  course  much  of  this  material  is 
in  a  highly  insoluble  condition,  but  though  attempts 
have  been  made  by  the  use  of  weak  acid  solvents  to 
discriminate  between  the  total  plant  food  in  the  soil  and 
that  portion  of  it  which  may  be  regarded  as  available  for 
the  plant,  no  proper  dividing  line  can  be  thus  drawn. 
The  availability  of  a  given  constituent,  say  of  phosphoric 
acid,  will  depend  upon  the  nature  of  the  crop.  A  given 
soil  may  contain  sufficient  easily  soluble  phosphoric 
acid  for  the  needs  of  the  wheat  plant  and  yet  fail 
to  supply  Swede  turnips  with  what  they  require. 
Again,  the  mechanical  texture  of  the  soil  may  be 
such  as  to  limit  the  root  range  of  the  plant,  so  that  a 
richer  soil  is  necessary  to  produce  as  good  results  as  are 
obtained  in  a  poorer  soil  of  more  open  structure ;  the 
state  of  the  micro-flora  of  the  soil  may  also  have  much 
to  do  with  the  amount  of  a  given  nutrient  that  can 
reach  the  plant. 

Perhaps  the  best  general  point  of  view  of  the  action 
of  fertilisers  is  obtained  by  extending  the  "  law  of  the 
minimum  "  originally  enunciated  by  Liebig,  according 
to  which  the  yield  of  a  given  crop  will  be  limited  by  the 
amount  of  the  one  particular  constituent  which  may 
happen  to  be  deficient ;  if  the  soil,  for  example,  is 
lacking  in  nitrogen,  the  yield  will  be  proportional  to  the 
supply  of  nitrogen  in  the  fertiliser,  and  no  excess  of 
other  constituents  will  make  up  for  the  shortage  of 
nitrogen.  To  take  an  example  from  the  Rothamsted 
experiments.  Table  LXXXVII.  shows  the  yield  of 
wheat    grain    and    straw   from    the    unmanured    plot, 


X.]  WHEAT  YIELD  WITH  INCREASED  NITROGEN  2^^ 

and  from  a  series  of  plots,  all  of  which  receive  an 
excess  of  phosphoric  acid,  potash,  etc.,  but  varying 
amounts  of  nitrogen,  ranging  from  43  lb.  to  172  lb. 
per  acre.  That  the  nitrogen  was  deficient  is  shown  by 
the  almost  negligible  increase  produced  by  the  mineral 
constituents  without  nitrogen ;  from  this  point  the 
increase  of  yield  is  roughly  proportional  to  the  supply 

Table  LXXXVI I.— Experiments  on  Wheat  (Broadbalk  Field, 
Rothamsted).    Averages  over  13  years  (1852-1864). 


Plot. 

Manures  per  acre. 

Dressed  Grain. 

Straw. 

Produce 

Increase 
for  each 
additional 

Produce 

Increase 

for  each 

additional 

per  acre. 

43  lb.  N. 
in  Manure. 

per  acre. 

43  lb.  N. 
in  Manure. 

Bushels. 

Bushels. 

Cwts. 

Cwts. 

3 

Unmanured 

15-6 

14-6 

.». 

5 

Minerals  alone 

18.3 

16.6 

... 

6 

Minerals  and  43  lb.  N. 

as  Ammonium  Salts. 

28-6 

IO-3 

27-1 

IO-5 

7 

Minerals  and  86  lb.  N. 

as  Ammonium  Salts . 

37-r 

8-5 

38-1 

II -o 

8 

Minerals  and  129  lb.  N. 

as  Ammonium  Salts. 

39-0 

1-9 

42-7 

4-6 

16 

Minerals  and  172  lb.  N. 

as  Ammonium  Salts. 

39-5 

0-5 

46-6 

3-9 

of  nitrogen,  until  it  reaches  an  excessive  amount.  The 
table  also  illustrates  the  generalisation  which  is  familiar 
to  economists  under  the  name  of  the  "  law  of  diminish- 
ing returns  " — that  the  first  expenditure  of  fertiliser  or 
other  factor  of  improvement  is  the  most  effective,  each 
succeeding  application  producing  smaller  and  smaller 
returns,  until  a  further  addition  causes  no  increase  in 
the  yield.  If  the  cost  of  the  fertiliser,  added  to  a 
prime  outlay  of  80s.  per  acre  for  the  cultivation, 
and  the  value  of  the  returns  in  cash,  are  expressed 
in  the  form  of  a  diagram,  the  law  is  clearly  expressed 


284  THEORIES  OF  FERTILISER  ACTION        [chap. 

by  the  series  of  curves  in  Fig.  5  ;  where  the  cost  of 
production  forms  a  straight  line  that  is  always  inter- 
sected by  the  curves  expressing  the  value  of  the  returns, 
which  begin  by  rising  more  rapidly  than  the  cost  of 
production,  but  tend  to  become  horizontal.  The  point 
of  intersection,  when  profit  ceases,  is  nearer  the  origin 
the  lower  the  range  of  prices  obtainable  for  the  crop, 
as  shown  by  the  two  curves  representing  the  returns  at 
low  and  high  prices  respectively ;  this  demonstrates  that 
the  expenditure  on  fertilisers  or  anything  else  required 
by  the  crop  must  be  reduced  when  prices  of  produce 
are  low,  or,  as  expressed  by  Lawes,  high  farming  is  no 
remedy  for  low  prices, 

Liebig's  law  of  the  minimum  must,  however,  be 
extended  to  all  the  factors  affecting  the  yield  as  well  as 
to  the  supply  of  plant  food,  e.g.,  to  such  matters  as  the 
supply  of  water,  the  temperature,  the  texture  of  the  soil. 
Any  one  of  these  may  be  the  determining  factor  which 
limits  the  yield,  or  two  or  more  of  them  may  act 
successively  at  different  periods  of  the  plant's  growth. 
On  poor  soils  the  water-supply  is  very  often  the  limiting 
factor — on  very  open  soils  because  the  water  actually 
drains  away,  on  extra  close  soils  because  the  root  range 
is  so  restricted  that  the  plant  has  but  little  water  at 
hand  and  the  movements  of  soil  water  to  renew  the 
supply  are  very  slow ;  in  either  case  for  comparatively 
long  periods  the  plant  will  be  sure  to  have  as  much 
nutriment  as  is  required  for  the  small  growth  permitted 
by  the  water  present.  It  is  only  when  the  water-supply 
is  sufficient  that  the  resources  of  the  soil,  as  regards  all 
or  any  of  the  constituents  of  a  fertiliser,  are  tested  and 
may  become  in  their  turn  the  limiting  factors  in  the 
growth  of  the  crop.  Hence  it  follows  that  fertilisers 
may  often  be  wasted  on  poor  land,  where  growth  is 
limited  by  the  texture  of  the  soil,  by  the  water-supply,  or 


Yield, 
ushels  or  Cwt. 


Returns    &  Cost. 
Shillings . 


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Returns  _at 

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at  Tow  "prices. 

Vlineral  Manures  +200  lb.        +400  lb.  +600  lb.         +800  lb.  Amm. Salts. 

Fig.  5.— Relation  between  Cost  of  Production  and  Returns  avith 
varying  (juantities  of  manure. 


[To  face  page  284. 


X.]  SOLUBILITY  OF  FERTILISERS  IN  SOIL  WATER  285 

by  some  other  factor  hardly  controllable  by  the  farmer : 
it  is  a  truism  that  poor  land  cannot  be  converted  into 
good  by  manuring  and  that  fertilisers  give  the  best 
returns  when  applied  to  a  good  soil. 

One  fundamental  difficulty  still  remains  in  consider- 
ing the  action  of  fertilisers ;  it  has  already  been  pointed 
out  that  a  soil  by  no  means  notably  fertile  may  contain 
enormous  quantities  of  plant  food,  which  is  however 
combined  in  so  insoluble  a  form  as  to  reach  the  plant 
in  quantities  insufficient  for  the  requirements  of  the 
crop.  For  example,  a  soil  may  contain  o-i  per  cent, 
or  2500  lb.  per  acre,  of  phosphoric  acid,  and  yet  yield  a 
very  indifferent  Swede  crop  unless  it  be  supplied  with 
an  additional  dressing  of  50  lb,  per  acre  of  soluble 
phosphoric  acid.  It  is  usually  assumed  that  the  effect 
of  this  phosphoric  acid  manuring  is  due  to  the  soluble 
nature  of  the  fertiliser,  because  of  which  the  additional 
plant  food  is  directly  available  for  the  crop.  But  a  little 
consideration  of  the  reactions  set  up  in  the  soil  will 
show  how  insufficient  such  a  theory  must  be ;  the 
phosphoric  acid  is  very  rapidly  precipitated  within  the 
soil,  as  is  shown  by  the  fact  that  on  many  soils  it 
remains  close  to  the  surface  for  many  years,  and  is 
never  washed  out  into  the  drains.  Bearing  in  mind 
this  precipitation  of  the  phosphoric  acid  in  an  in- 
soluble condition,  Whitney  and  Cameron  argue  that 
previous  to  the  addition  of  the  fertiliser  a  certain 
amount  of  phosphoric  acid  exists  in  solution  in  the  soil 
water,  this  amount  being  in  equilibrium  with  the  various 
phosphates  of  calcium,  iron,  aluminium,  etc.,  making  up 
the  great  store  of  phosphates  in  the  soil.  This  particular 
state  of  equilibrium  would  be  but  little  disturbed  by  the 
addition  of  the  soluble  fertiliser  in  quantities  which  are 
small  compared  with  the  great  mass  of  undissolved 
phosphates  in  contact  with  the  soil  water ;  the  added 


286  THEORIES  OF  FERTILISER  ACTION       [chap. 

phosphoric  acid  would  only  displace  an  almost  equivalent 
amount  of  the  phosphoric  acid  already  in  solution,  and 
the  concentration  of  the  new  solution  would  only  differ 
from  the  old  in  the  same  degree  as  the  ratio  of  the 
phosphoric  acid  in  the  soil  plus  fertiliser  (2500+50  lb. 
of  phosphoric  acid),  bears  to  the  phosphoric  acid 
originally  in  the  soil  (z>.,  2500  lb.  phosphoric  acid).  In 
other  words,  before  the  fertiliser  was  added,  the  soil 
water  was  as  fully  saturated  with  phosphoric  acid  as 
the  amount  of  calcium,  iron,  aluminium,  and  other  bases 
would  permit,  and  as  these  bases  are  present  in  enormous 
excess,  the  soil  water  must  remain  at  the  same  satura- 
tion point  after  the  fertiliser  has  been  added,  just  as 
water  will  only  hold  35  per  cent,  of  common  salt  in 
solution  with  however  large  a  quantity  of  salt  it  may 
be  in  contact.  In  the  same  way  the  soil  contains 
certain  double  silicates  of  which  potassium  is  a  con- 
stituent, and  these  hydrolise  to  a  slight  extent  in  contact 
with  the  soil  water  to  yield  a  solution  containing 
potassium  ions.  The  addition  of  a  soluble  potassium 
salt,  as  in  a  fertiliser,  will  diminish  the  dissociation  and 
therefore  the  solubility  of  the  double  silicate,  the 
potassium  of  which  is  thrown  out  of  solution ;  until,  as 
Whitney  and  Cameron  argue,  no  more  potassium  ions 
remain  in  solution  than  were  present  before  the  addition 
of  the  fertiliser.  According  to  this  point  of  view,  the 
concentration  of  the  soil  water  for  a  given  plant  food, 
such  as  phosphoric  acid,  must  be  approximately  constant 
for  all  soils  of  the  same  type,  however  much  or  little 
phosphatic  fertiliser  may  have  been  applied,  and  since 
water  culture  experiments  show  that  this  low  limit  of 
concentration  attained  by  the  soil  water  is  more  than 
sufficient  for  the  needs  of  the  plant,  no  soil  can  be 
regarded  as  deficient  in  this  or  any  other  element  of 
plant  food.     It  therefore  follows  that  the  action,  if  any, 


X.]  FERTILISING  CONSTITUENTS  IN  SOIL  WATER  287 

of  a  fertiliser  must  be  due  to  some  other  cause  than  the 
direct  supply  of  plant  food,  with  which  the  soil  water 
must  always  be  saturated  to  a  degree  which  is  quite 
unaffected  by  the  supply  of  fertiliser. 

This  view  of  the  interactions  between  the  sparingly 
soluble  phosphates  of  the  soil,  the  soil  water,  and  the 
added  soluble  fertiliser  can  hardly  be  regarded  as  valid 
in  theory,  even  if  the  conditions  under  which  the 
reagents  exist  in  the  soil  were  the  same  as  those 
which  prevail  in  the  laboratory  when  such  states  of 
equilibrium  between  sparingly  soluble  solids  and  water 
are  worked  out.  It  has  no  bearing  whatever  on  the 
amount  of  nitrates  in  the  soil  water,  since  they  come 
into  a  dissolved  state  as  fast  as  the  nitrifying  bacteria 
produce  them  and  are  not  in  equilibrium  with  any  store 
of  undissolved  nitrates  in  the  background.  As  regards 
phosphoric  acid,  the  theory  assumes  such  an  excess  of 
bases  that  all  soils  behave  alike  in  immediately  pre- 
cipitating the  phosphoric  acid  in  the  same  form ; 
while  as  regards  potash,  the  argument  seems  to 
forget  that  though  the  addition  of  a  soluble  potassium 
salt  may  throw  some  of  the  other  sparingly  soluble 
potassium  compounds  out  of  solution,  the  total  amount 
of  potassium  remaining  in  solution  will  still  be  greatly 
increased.  The  function  of  the  carbonic  acid  in  the  soil 
water  is  ignored,  as  also  is  the  fact  that  the  processes 
of  solution  in  the  soil  must  be  in  a  constant  state  of 
change,  so  that  it  is  the  rate  at  which  the  constituents 
go  into  solution  rather  than  the  actual  amount  dissolved 
at  any  given  moment  which  is  of  importance.  The  soil 
is  too  complex  a  mixture  to  permit  as  yet  of  attaching 
great  weight  to  theoretical  deductions  as  to  the  actions 
taking  place  in  it,  and  that  the  state  of  affairs  postulated 
by  Whitney  and  Cameron  does  hold  in  the  soil,  has 
not  however  been  verified  by  experiment ;  the  analyses, 


288  THEORIES  OF  FERTILISER  ACTION        [chap. 

given  by  the  authors  of  the  theory,  of  the  cold  water 
extracts  from  a  number  of  soils  show  great  variations  in 
their  concentration  in  nitrates,  phosphoric  acid,  and 
potash;  nor  is  any  evidence  forthcoming  that  such 
concentrations  are  not  immediately  raised  by  the 
addition  of  fertilisers.  Indeed,  when  the  Rothamsted 
soils,  with  their  long-continued  differences  in  fertiliser 
treatment,  are  extracted  with  water  charged  with 
carbon  dioxide — the  nearest  laboratory  equivalent  to 
the  actual  soil  water — the  amount  of  phosphoric  acid 
going  into  solution  is  closely  proportional  to  the 
previous  fertiliser  supply,  and  this  proportionality  is 
maintained  if  the  extraction  is  repeated  with  fresh 
solvent,  as  must  be  the  case  in  the  soil.  In  the  field  it 
is  not  merely  the  initial  concentration  of  the  soil  water 
in  plant  food  which  determines  the  supply  of  nutriment 
to  the  crop ;  it  is  also  the  capacity  of  the  soil  to  keep 
renewing  the  solution  as  the  plant  withdraws  from  it 
the  essential  elements. 

In  one  essential  respect  again  the  conditions  pre- 
vailing in  the  soil  are  very  different  from  those  of  the 
laboratory.  In  the  soil  all  reactions  are  extremely 
localised,  since  they  take  place  in  the  thin  film  of  water 
normally  surrounding  the  soil  particles,  in  which 
movement  of  the  dissolved  matter  takes  place  very 
slowly,  mainly  by  diffusion.  Of  the  extreme  slow- 
ness of  the  diffusion  of  soluble  salts  in  the  soil  the 
Rothamsted  experiments  afford  some  good  examples. 
For  instance,  on  the  grass  plots  only  an  imaginary  line 
divides  the  plots  receiving  different  fertilisers ;  the 
manure  is  sown  right  up  to  the  edge  of  the  plot,  a 
screen  being  placed  along  the  edge  to  prevent  any 
being  thrown  across  the  boundary,  then  immediately 
on  the  other  side  of  the  boundary  the  different  treat- 
ment begins.     In  two  cases  plots  receiving  very  large 


X.]    SLOW  DIFFUSION  OF  FERTILISERS  IN  SOIL  289 

amounts  of  soluble  fertiliser,  e.g.,  550  lb.  per  acre  of 
nitrate  of  soda,  or  600  lb.  per  acre  of  ammonium  salts, 
march  with  plots  receiving  either  no  fertiliser  or  a 
characteristically  different  one,  yet  in  neither  case  is 
there  any  sign  in  the  herbage  that  the  soluble  fertiliser 
has  diffused  over  the  boundary.  Although  the  treat- 
ment has  been  repeated  now  for  fifty-two  years, 
the  dividing  line  between  the  two  plots  remains  per- 
fectly sharp,  and  the  rank  herbage  produced  by  the 
excess  of  nitrogenous  fertiliser  on  one  side  does  not  stray 
6  inches  over  the  boundary.  Again,  on  the  Rotham- 
sted  wheatfield  the  plots  were  24-7  feet  in  breadth, 
and  were  separated  by  unfertilised  strips  only  about  a 
foot  in  breadth;  in  1893,  each  plot  was  sampled  down 
to  a  depth  of  7-5  feet,  and  the  amount  of  nitrates  was 
determined  in  each  successive  sample  of  9  inches  in 
depth.  The  amount  of  nitrates  found  was  in  each  case 
characteristic  of  the  supply  of  nitrogen  to  the  surface  of 
the  plot,  and  right  down  to  the  lowest  depth  there  were 
no  signs  of  the  proportions  approximating  to  a  common 
level,  as  they  would  have  done  had  any  considerable 
amount  of  lateral  diffusion  been  taking  place.  Con- 
sidering that  the  plots  are  only  separated  by  a  foot  or 
so  of  soil,  and  each  had  been  receiving  its  particular 
amount  of  nitrogen  for  forty  and  in  some  cases  for  fifty 
years,  the  sharp  differentiation  of  plot  from  plot  in  the 
amount  of  nitrates  at  a  depth  of  7  feet  is  sufficiently 
remarkable,  and  is  evidence  that  the  movements  of  the 
soluble  salts  in  the  soil  are  almost  wholly  confined  to 
up  and  down  motions  due  to  percolation  and  capillary 
uplift,  lateral  diffusion  taking  place  only  to  an  insignifi- 
cant extent. 

From  these  considerations  we  may  conclude  that 
when  a  fertiliser  is  mixed  with  the  soil,  each  particle 
will  establish  round  itself  a  zone  of  a  comparatively 

T 


290  THEORIES  OF  FERTILISER  ACTION       [chap. 

concentrated  solution,  to  which  the  plant's  roots  will  be 
drawn  by  the  ordinary  chemiotactic  actions,  and  that 
these  zones  will  extend  but  a  little  way  into  the 
generally  much  less  dilute  mass  of  the  soil  water, 
because  of  the  slowness  of  the  diffusion  process. 

That  some  such  state  of  things  prevails  in  the  soil 
may  be  surmised  from  the  common  farming  experience 
of  the  benefits  derived  from  sowing  the  fertiliser  close 
to  the  seed,  as  when  superphosphate  is  sown  with  turnip 
seed,  because  in  that  case  the  fertiliser  is  not  injurious 
to  germination  and  the  young  plant  is  specially  dependent 
on  being  rapidly  pushed  into  growth  in  the  early  stages. 
Again,  the  intimate  way  in  which  the  feeding  fibrous 
roots  of  a  plant  will  surround  and  cling  to  a  fragment  of 
fertiliser  in  the  soil,  such  as  a  bone  or  a  piece  of  shoddy, 
shows  that  some  other  actions  are  at  work  in  the  soil 
than  the  feeding  of  the  plant  upon  the  nutrients  con- 
tained in  the  general  soil  solution. 

Whitney  and  Cameron's  theory  also  supposes  that 
the  plant  itself  exerts  no  solvent  action,  whereas  it  has 
often  been  supposed  that  the  roots  excrete  substances 
of  an  acid  nature  which  exert  a  solvent  action  upon  the 
soil  particles.  In  this  direction  an  experiment  of  Sachs' 
has  become  classical.  He  took  a  slab  of  polished  marble 
and  set  it  vertically  in  a  pot  of  soil  in  which  beans  or 
some  kindred  plant  were  grown.  After  the  plants  had 
been  growing  for  some  time  the  contents  of  the  pot 
were  turned  out  and  the  slab  of  marble  washed,  where- 
upon the  polished  surface  was  found  to  be  etched 
wherever  the  roots  had  been  growing  in  contact  with 
it.  A  polished  slab  of  gypsum  similarly  treated  shows 
a  raised  pattern  wherever  the  roots  have  protected  the 
surface  from  the  solvent  action  of  the  general  mass  of 
water  in  the  soil.  Although  Sachs  himself  attributed 
the  etching  to  the  action  of  the  carbon  dioxide  which  is 


X.]  EXCRETIONS  FROM  PLANT  ROOTS  291 

alwaj's  being  given  off  by  the  roots,  it  has  also  been  set 
down  to  fixed  acids  excreted  by  the  root  hairs,  and 
determinations  have  been  made  of  the  acidity  of  the 
sap  of  the  roots  with  the  idea  of  differentiating  between 
the  solvent  power  of  various  plants.  The  roots  of 
germinating  seedlings  are  also  found  on  occasion  to 
redden  blue  litmus  paper,  and  undoubtedly  may  excrete 
substances  of  an  acid  character,  but  the  behaviour  of 
seedlings,  which  are  building  up  their  fresh  tissue  out 
of  the  broken-down  reserve  materials  contained  in  the 
seed,  is  essentially  different  from  that  of  plants  leading 
an  independent  existence,  so  that  nothing  is  thereby 
proved  as  to  the  source  of  the  etching  in  Sachs' 
experiments. 

Czapek  instituted  a  fresh  series  of  experiments  with 
smooth  slabs  prepared  by  floating  on  to  glass  plates 
mixtures  of  plaster  of  Paris  and  various  phosphates 
of  calcium,  iron,  and  aluminium ;  since  the  iron  and 
aluminium  phosphates  were  attacked,  most  of  the  possible 
acids  were  excluded,  and  the  etching  action  of  the  plant's 
roots  could  only  be  due  to  carbon  dioxide  or  acetic  acid. 
The  latter  was  again  excluded  by  a  further  experiment  in 
which  the  slab  was  coloured  with  Congo  red,  and  as  this 
was  not  affected  the  sole  remaining  solvent  body  the 
plant  could  have  excreted  was  carbon  dioxide.  Again, 
it  has  already  been  shown  that  water  cultures  containing 
nitrates,  where  the  plant  is  growing  in  such  solutions  as 
exist  under  normal  soil  conditions,  tend  to  become 
alkaline  instead  of  acid,  so  that  the  balance  of  evidence 
is  against  the  idea  that  plant  roots  excrete  any  fixed 
acids  exerting  a  solvent  action  upon  the  soil  particles. 
The  carbon  dioxide,  however,  probably  exerts  a  con- 
siderable action,  especially  in  the  immediate  vicinity  of 
the  root  from  which  it  is  given  off,  for  as  it  passes 
through   the   cell    wall   it   must   momentarily    form    a 


292  THEORIES  OF  FERTILISER  ACTION       [chap, 

solution  of  considerable  concentration'  possessing  a 
proportionally  increased  solvent  power,  and  it  is  to  this 
supersaturated  solution  that  may  be  attributed  the 
highly  localised  attack  of  the  roots  upon  the  soil 
particles.  An  experiment  by  Kossowitsch  illustrates 
the  part  played  by  the  roots  in  attacking  the  insoluble 
materials  in  the  soil :  two  pots  of  sand  were  prepared, 
each  mixed  with  the  same  quantity  of  calcium 
phosphate  in  the  form  of  ground  rock  phosphate,  a  third 
pot  contained  sand  only.  In  this  latter  and  in  one  of 
the  pots  containing  the  calcium  phosphate,  seeds  of 
mustard,  peas,  and  flax  were  sown.  The  growing  plants 
were  then  furnished  with  a  slow  continuous  supply  of 
water  containing  appropriate  amounts  of  nitrates, 
potash,  and  other  nutrient  salts  except  phosphates. 
Before,  however,  this  nutrient  solution  reached  the  pot 
containing  the  sand  only,  it  was  made  to  percolate 
through  the  second  pot  containing  sand  and  calcium 
phosphate,  but  it  was  applied  directly  to  the  pot  con- 
taining calcium  phosphate.  In  the  pot  containing 
calcium  phosphate,  the  growth  was  much  greater  than 
in  the  other  pot,  where  the  nutrient  solution  only  con- 
tained what  phosphoric  acid  it  could  dissolve  in  its 
passage  over  the  calcium  phosphate  in  the  pot  in  which 
nothing  was  growing,  although  this  solution  was 
continually  renewed.  The  only  factor  determining  the 
supply  of  phosphoric  acid  and  the  consequent  difference 
in  growth  was  the  solvent  action  of  the  roots  when 
they  were  actually  in  contact  with  the  calcium 
phosphate,  and  this  solvent  action,  as  has  already  been 
shown,  may  most  probably  be  attributed  to  the  carbon 
dioxide  they  excreted. 

Following  up  their  conclusions  that  the  soil  water 
possesses  an  approximately  constant  composition  under 
all   circumstances   and   always   contains    more   of   the 


X.]  EXCRETION  OF  TOXIC  SUBSTANCES  293 

constituents  of  plant  food  than  would  be  required  for 
the  nutrition  of  the  plant,  Whitney  and  his  colleagues 
have  suggested  another  theory  of  fertiliser  action. 
According  to  this  point  of  view,  a  soil  falls  off  in  fertility 
and  ceases  to  yield  normal  crops,  not  because  of  any 
lack  of  plant  food  brought  about  by  the  continuous 
withdrawal  of  the  original  stock  in  the  soil,  but  because 
of  the  accumulation  of  injurious  substances  excreted 
from  the  plant  itself  These  toxins  are  specific  to  each 
plant  but  are  gradually  removed  from  the  soil  by 
processes  of  decay,  so  that  if  a  proper  rotation  of  crops 
be  practised,  to  ensure  that  the  same  plant  only  recurs 
after  an  interval  long  enough  to  permit  of  the  destruc- 
tion of  its  particular  self-formed  toxin,  its  yield  will  be 
maintained  without  the  intervention  of  fertilisers.  The 
function  of  fertilisers  is  to  precipitate  or  to  put  out  of 
action  these  toxins,  and  various  bodies  such  as  lime, 
green  manure,  and  ferric  hydrate  are  also  effective  in 
this  direction ;  the  same  result  of  destruction  of  the 
toxins  excreted  by  the  plant  may  even  be  brought  about 
by  minute  quantities  of  certain  bodies  like  pyrogallol. 
According  to  this  theory  the  function  of  fertilisers  is  to 
remove  toxins  rather  than  to  feed  the  plant :  they  are 
only  required  when  the  same  crop  is  grown  continuously, 
and  the  need  for  them  may  be  obviated  by  a  judicious 
rotation  which  permits  of  the  destruction  of  the  toxins 
by  natural  causes.  Careful  consideration  will  show 
that  this  theory  can  be  made  to  fit  a  good  many  of  the 
phenomena  of  plant  nutrition,  it  would  also  explain  the 
difficulties  experienced  in  growing  certain  crops  con- 
tinuously on  the  same  ground  ;  it  is  in  fact  an  elaborated 
revival  of  one  of  the  earliest  explanations  of  the  value 
of  rotations,  originally  suggested  by  de  Candolle. 
Furthermore,  Whitney's  colleagues  have  succeeded  in 
extracting  certain  substances  from  the  soil — di-hydroxy- 


294  THEORIES  OF  FERTILISER  ACTION       [chap. 

stearic  acid,  picoline-carboxylic  acid,  etc.,  which  when 
introduced  into  water  cultures  are  toxic  to  seedling 
plants.  The  compounds  isolated  are,  however,  all  of 
them  products  of  the  oxidation  and  decay  of  proteins, 
fats,  and  other  compounds  contained  in  plant  residues  ; 
there  is  no  evidence  to  show  that  they  are  specific 
excretions  from  particular  plants  or  that  they  are  more 
abundant  in  soil  impoverished  by  the  continuous 
growth  of  a  crop  than  in  soil  which  would  be  usually 
termed  rich.  Again,  it  has  not  been  demonstrated  that 
such  substances,  although  harmful  to  young  plants  in 
water  culture,  are  toxic  under  soil  conditions  ;  it  is  well 
known  how  exceedingly  sensitive  are  plants  in  water 
culture,  where  growth,  for  example,  is  inhibited  by 
traces  of  copper  not  to  be  detected  by  ordinary  methods 
of  analysis.  A  body  like  ammonia,  itself  a  product  of 
protein  decay  and  present  in  the  soil,  is  exceedingly 
toxic  to  water  cultures,  yet  when  applied  to  the  soil  it 
increases  the  growth  of  the  plant.  Turning  to  the 
fertiliser  side  of  the  theory,  evidence  is  yet  lacking  to 
show  that  fertilisers  in  such  dilute  solutions  as  they 
form  in  the  soil  water  can  exert  any  precipitating  or 
destructive  action  on  such  toxic  substances  as  have 
been  extracted  from  the  soil ;  particularly  the  specific 
action  of  fertilisers  is  difficult  to  explain.  Why  should 
substances  so  dissimilar  as  nitrate  of  soda  and 
sulphate  of  ammonia  exert  the  same  sort  of  action  on 
the  same  toxin  ?  Why  should  phosphates  cause  all 
classes  of  plants  to  develop  in  one  direction,  or  why 
should  they  be  appropriate  to  the  toxins  of  all  plants 
on  one  particular  type  of  soil,  whereas  potash  answers 
on  another  soil  type? 

Lastly,  there  is  a  lack  of  evidence  for  the  funda- 
mental thesis  that  the  rotation  will  take  the  place 
pf  fertilisers  and  that  the  yield  only  falls  off  when   a 


X.]      CAN  ROTA  TIONS  REP  LA  CE  PER  TILISERS  ?     29  \ 

particular  crop  is  grown  continuously  on  the  same  land. 
On  the  rotation  field  at  Rothamsted  the  yield  of 
wheat  on  the  unfertilised  plot  has  been  remarkably 
maintained ;  for  the  last  five  courses  (loth  to  14th  of 
the  whole  series)  it  has  averaged  26-2  bushels  per  acre, 
but  it  is  below  the  yield  of  the  fertilised  plots  on  the 
Broadbalk  field,  which  averaged  35-7,  32,  and  39-7 
bushels  for  the  same  years,  and  also  below  the  fertilised 
plot  on  the  same  rotation  field,  which  averaged  for  the 
same  period  37-1  bushels  per  acre,  although  the  fertiliser 
is  only  applied  once  in  four  years  to  the  Swedes,  which 
are  followed  by  barley  and  either  clover  or  a  bare  fallow 
before  the  turn  of  the  wheat  comes  round.  But  with 
other  crops  than  wheat  no  such  maintenance  of  yield  is 
to  be  seen  on  the  unfertilised  plot  of  the  rotation  field — 
the  barley  yield  has  been  reduced  to  15-8  bushels 
against  27-7  on  the  fertilised  plot,  the  clover  yield  to 
94  cwts.  against  37-8  on  the  fertilised  plot,  and  the 
turnips  to  as  little  as  16  cwts.  against  400  on  the 
fertilised  plot.  Here  we  see  that  with  the  barley,  clover, 
and  particularly  with  the  turnip  crop,  a  rotation  is  quite 
unable  to  do  the  work  of  the  fertiliser ;  the  yield  of 
turnips  is  reduced  to  a  minimum  on  the  impoverished 
soil,  even  though  the  crop  only  comes  round  once  in 
four  years  and  then  grows  so  poorly  that  it  can  do  little 
specific  excretion  to  harm  the  succeeding  crop.  Many 
instances  could  be  given  of  the  incapacity  of  certain 
plants  to  grow  in  soil  the  fertility  of  which  had  been 
exhausted  by  other  crops  ;  for  example,  at  Rothamsted 
in  1903,  Swede  turnips  were  sown  on  Little  Hoos  field, 
which  was  known  not  to  have  been  cropped  with  Swedes 
or  any  kindred  crop  for  more  than  forty  years,  and  the 
average  yield  from  thirty-two  unmanured  plots  was  only 
9-3  tons  per  acre,  although  an  exceptionally  good  start 
was  made  by  the  plant.     In  the  following  season  barley 


296  THEORIES  OF  FERTILISER  ACTION       [chap. 

was  grown  and  the  unmanured  plots  averaged  24-2 
bushels  per  acre,  a  relatively  much  higher  yield  than 
the  Swedes  had  shown — yet  barley  had  been  repeatedly 
grown  on  the  field  in  the  years  immediately  before  it 
was  brought  under  experiment. 

As  it  stands  at  present  Whitney's  theory  must  be 
regarded  as  lacking  the  necessary  experimental  founda- 
tion ;  no  convincing  evidence  has  been  produced  of  the 
fundamental  fact  of  the  excretion  of  toxic  substances 
from  plants  past  the  autotrophic  seedling  stage,  nor  is 
there  direct  proof  of  the  initial  supposition  that  all  soils 
give  rise  to  soil  solutions  sufficiently  rich  in  the  elements 
of  plant  food  to  nourish  a  full  crop,  did  not  some  other 
factor  come  into  play.  If,  however,  we  give  the  theory 
a  wider  form,  and  instead  of  excretions  from  the  plant 
understand  debris  of  any  kind  left  behind  by  the  plant 
and  the  results  of  bacterial  action  upon  it,  we  may 
thereby  obtain  a  clue  to  certain  phenomena  at  present 
imperfectly  understood.  The  value  of  a  rotation  of 
crops  is  undoubted  and  in  the  main  is  explicable  by  the 
opportunity  it  affords  of  cleaning  the  ground,  the 
freedom  from  any  accumulation  of  weeds,  insect,  or 
fungoid  pests  associated  with  a  particular  crop,  and  to 
the  successive  tillage  of  different  layers  of  the  soil,  but 
for  many  crops  there  remains  a  certain  beneficial  effect 
from  a  rotation  beyond  the  factors  enumerated. 

The  Rothamsted  experiments  have  shown  that 
wheat  can  be  grown  continuously  upon  the  same  land 
for  more  than  fifty  years,  and  that  the  yield  when 
proper  fertilisers  are  applied  remains  as  large  in  the 
later  as  in  the  earlier  years  of  the  series ;  any  decline 
that  is  taking  place  is  hardly  outside  the  limits  of 
seasonal  variation  and  can  easily  be  accounted  for  by 
the  difficulties  of  tillage  and  the  increase  of  one  or  two 
troublesome  weeds.    Mangolds,  again,  in  the  Rothamsted 


X.]  VALUE  OF  ROTATION  OF  CROPS  297 

experiments  show  no  falling  off  in  yield,  though  they 
have  now  been  grown  upon  the  same  land  for  thirty- 
two  years  ;  but  with  the  barley  crop,  despite  the  applica- 
tion of  fertilisers,  there  is  a  distinct  secular  decline  in 
the  yield.  Again,  it  was  found  impossible  to  obtain 
satisfactory  crops  of  Swede  turnips  upon  the  same  land 
for  more  than  ten  or  twelve  years  in  succession,  and 
clover  is  well  known  to  render  the  land  "  sick "  for  its 
own  renewed  growth  for  a  period  of  from  four  to  eight 
years  on  British  soil.  In  this  last  case  the  persistence 
of  the  resting  stages  of  the  sderotinia  disease  in  the 
land  may  be  the  determining  factor,  but  there  are  other 
crops,  e.g.,  flax,  hemp,  and  strawberries,  which  are  con- 
sidered by  the  practical  cultivator  to  render  the  land 
more  or  less  "  sick,"  so  that  their  growth  cannot  profit- 
ably be  renewed  until  an  interval  of  some  years  has 
elapsed. 

Again,  it  is  well  known  that  when  a  plant  is  sown 
upon  land  which  has  not  carried  that  particular  crop  for 
many  years  beforehand,  it  starts  into  growth  with  a 
vigour  it  rarely  displays  upon  land  where  it  forms  an 
item  in  the  regular  rotation,  even  though  the  new  land 
is  so  impoverished  that  the  final  yield  is  indifferent 
In  the  instance  quoted  above,  where  Swedes  were 
sown  on  the  Little  Hoos  field  after  a  very  long 
interval,  although  the  yield  was  poor  on  the  unmanured 
plots  yet  the  seeds  germinated  and  made  their  early 
growth  in  a  very  remarkable  fashion,  incomparably 
better  than  did  the  same  seed  sown  upon  adjoining 
land  in  a  high  state  of  fertility,  but  which  had  been 
cropped  with  Swedes  from  time  to  time  previously. 
There  is  thus  some  positive  evidence  that  most  plants 
— some  to  a  very  slight  degree,  like  wheat  and  mangolds, 
others  markedly,  like  clover,  turnips,  and  flax — effect 
some  change  in  the  soil  which  unfits  it  for  the  renewed 


298         THEORIES  OF  FERTILISER  ACTION        [chap. 

growth  of  the  crop.  The  injurious  action  may  even 
arise  from  the  growth  of  a  different  crop,  as  in  the  well- 
known  experiments  at  the  Woburn  Fruit  Farm,  where 
Pickering  has  shown  that  the  roots  of  grasses  exert  a 
positively  injurious  effect,  distinct  from  competition  for 
food,  water,  or  air,  upon  fruit  trees  growing  in  the  same 
soil. 

Assuming  that  the  persistence  in  the  soil  of  obscure 
diseases  appropriate  to  the  particular  plant  can  be 
neglected  as  the  cause  of  these  phenomena,  there  still 
remains  some  unexplained  factor  arising  from  a  plant's 
growth  which  is  injurious  to  a  succeeding  crop,  and  this 
may  either  be  the  excreted  toxins  of  Whitney's  theory 
or  may  be  some  secondary  effects  due  to  the  competi- 
tion or  injurious  products  of  the  bacteria  and  other 
micro-flora  accumulated  in  the  particular  soil  layer  in 
which  the  roots  of  the  crop  chiefly  reside.  Experi- 
mental evidence  is  as  yet  wanting  as  to  these  highly 
complex  interactions  between  the  higher  plants  and 
the  micro-flora  of  the  soil,  but  Russell  and  other 
observers  have  shown  how  greatly  a  disturbance  of  the 
normal  equilibrium  of  the  flora  of  the  soil  may  affect  its 
fertility,  as  measured  by  the  yield  of  a  higher  plant 
Partial  sterilisation,  such  as  is  brought  about  by  heating 
the  soil  to  98°  for  ten  hours,  will  double  the  yield  of  the 
succeeding  crop  and  will  show  a  perceptible  beneficial 
effect  up  to  the  fourth  crop  after  the  heating;  and 
exposure  to  the  vapours  of  volatile  antiseptics  like 
toluene  or  carbon  bisulphide,  which  are  afterwards 
entirely  removed  by  exposure,  will  increase  the  yield  in 
a  similar  but  smaller  degree ;  even  drying  the  soil 
appears  to  have  an  influence  upon  its  fertility. 

It  is  in  this  direction  perhaps  that  the  clue  may  be 
found  to  the  unexplained  benefits  of  the  rotation  of 
crops,  and  to  some  of  the  other  facts  difficult  of  ex- 


X.]  VALUE  OF  ROTATION  OF  CROPS  1C)C) 

planation  upon  the  ordinary  theories  of  plant  nutrition 
which  have  been  advanced  by  Whitney  and  his  co- 
workers. The  soil  however  is  such  a  complex  medium 
— the  seat  of  so  many  and  diverse  interactions,  chemical, 
physical,  and  biological — and  is  so  unsusceptible  of 
synthetic  reproduction  from  known  materials,  that 
experimental  work  of  a  crucial  character  becomes 
extremely  difficult  and  above  all  requires  to  be  inter- 
Dieted  with  extreme  caution  and  conservatism 


CHAPTER  XI 

SYSTEMS    OF    MANURING   CROPS 

High  and  Low  Farming — Fertilising  Constituents  removed  in 
Meal  and  Corn — Losses  of  Nitrogen  increased  when  Land  is 
in  High  Condition — Manures  for  Wheat — Barley  :  Importance 
of  Quality — Oats — Root  Crops  :  Swedes,  Mangolds,  Potatoes 
— Importance  of  Farmyard  Manure  for  Root  Crops — 
Leguminous  Crops :  Beans,  Clover,  Lucerne,  Sainfoin — 
Value  of  Potassic  Fertilisers — Grass  Land — Effect  of  Manures 
in  changing  the  Botanical  Character  of  the  Herbage — Land 
laid  up  for  Hay — Manures  for  Poor  Pastures — Hops — Fruit — 
Garden  Manures — Manures  for  Tropical  and  Semi-Tropical 
Crops :  Sugar  Cane,  Tobacco,  Cotton,  Tea. 

In  dealing  with  the  specific  properties  of  the  various 
fertilisers,  a  number  of  illustrations  have  been  given 
from  the  results  of  field  experiments  on  particular  crops 
from  which  conclusions  might  be  drawn  as  to  the 
fertilisers  most  appropriate  to  those  crops,  but  in  the 
main  these  experiments  have  been  selected  to  illustrate 
the  action  of  the  fertiliser  rather  than  the  requirements 
of  the  plant.  It  remains  to  reconsider  the  information 
derived  from  experiments  under  its  practical  aspect,  so 
as  to  obtain  a  guide  to  the  methods  of  manuring  which 
the  farmer  should  adopt  for  the  crops  he  is  setting  out 
to  grow.  It  is  never  possible  to  do  this  absolutely ;  the 
proper  manure  for  any  particular  crop  must  always  be 
conditioned  by  a  number  of  local  circumstances  special 
to  the  farm  in  question  ;  from  which  it  follows  that  the 

900 


CHAP.  XI.]  SYSTEMS  Of  FARMING  301 

mixtures  sold  as  "  Turnip  Manures,"  "  Potato  Manures," 
and  so  forth,  must  be  in  the  majority  of  cases  more  or 
less  wasteful  if  they  are  to  be  effective  everywhere. 
Instead  of  applying  a  kind  of  average  manure,  the  farmer 
ought  to  have  such  an  appreciation  of  manurial  principles 
that  he  can  adapt  his  fertilisers  as  economically  as 
possible  to  his  own  soil  and  conditions  of  farming. 

In  discussing  the  application  of  fertilisers  to  crops, 
even  when  the  special  features  presented  by  the  soil  are 
neglected,  we  can  draw  no  conclusions  as  to  the  proper 
methods  of  manuring  unless  we  take  into  account  the 
place  the  crop  occupies  in  the  rotation  adopted  by  the 
farmer,  and  also  the  character  of  his  land  and  style  of 
farming.  For  example,  we  have  not  to  consider  the 
wheat  crop  as  standing  by  itself  in  the  manner  we  see 
it  in  the  Rothamsted  experiments,  but  as  it  is  generally 
grown  in  practice — after  a  clover  crop,  or  perhaps  after 
mangolds  which  have  been  manured  with  dung. 
Furthermore,  one  man  may  be  in  possession  of  good 
land  in  high  condition,  and  may  be  farming  "high"  for 
big  crops ;  he  will  be  justified  in  a  greater  outlay  upon 
fertilisers  than  would  be  advisable  for  an  equally  good 
farmer  on  poorer  land,  where  it  may  be  more  economical 
to  be  content  with  smaller  crops  and  to  keep  down  the 
expenditure.  The  manuring  to  be  adopted  on  a  given 
farm  must  be  looked  at  as  a  whole,  as  a  system  to  be 
shaped  as  much  by  various  wider  considerations  of 
farming  policy  as  by  the  particular  crops  that  are  being 
grown.  It  is  easy,  for  example,  to  indicate  the  com- 
position a  manure  for  Swedes  should  possess,  but 
whether  a  farmer  should  spend  15s.  or  40s.  an  acre  on 
fertilisers  for  his  Swede  land  depends  entirely  upon  the 
general  character  and  style  of  his  farm.  It  is  for 
this  reason  that  many  field  experiments,  however 
ostensibly  designed  on  a  cash  basis  to  show  the  returns 


302  SYSTEMS  OF  MANURING  CROPS         [chap. 

for  a  given  outlay  in  manure,  are  really  unpractical ;  so 
variable  is  the  basis — the  condition  of  the  land — upon 
which  the  return  depends,  and  so  much  does  the  power 
of  realising  products  like  roots  change  from  farm  to 
farm.  The  style  of  farming,  and  with  it  the  amount  of 
fertilisers  that  can  be  profitably  employed,  will  always 
be  dictated  by  such  local  conditions  as  the  markets 
available,  the  supply  of  labour,  and  the  rent  of  the  land. 
On  the  one  hand  we  have  the  systems  prevailing  in  the 
middle  west  of  America  and  other  more  newly  settled 
countries  where  the  farmer  is  living  upon  the  capital 
originally  stored  up  in  the  virgin  soil.  He  grows,  for 
example,  maize  and  wheat  alternately,  using  no  fertiliser 
and  restoring  nothing  to  the  soil,  often  burning  the 
straw  and  not  even  taking  the  trouble  to  cart  out 
the  manure  accumulated  beneath  any  cattle  he  may 
feed.  Year  after  year  50  to  100  lb.  of  nitrogen  per  acre 
are  being  removed  and  the  soil  is  getting  steadily 
poorer,  yet  it  has  proved  to  be  more  profitable  to  move 
to  fresh  land  than  to  spend  money  in  restoring  the  lost 
fertility.  On  the  other  hand,  in  many  parts  of  Great 
Britain  we  may  see  a  strictly  conservative  system  at 
work.  The  land  possesses  a  certain  condition  and  will 
yield  fair  average  crops,  only  part  of  which  are  sold — 
the  wheat  and  barley — the  rest  are  converted  into  meat 
and  dung,  by  which  means  the  greater  part  of  the  plant 
food  drawn  from  the  soil  is  returned.  There  is,  however, 
a  certain  removal  in  the  corn  and  meat  and  a  certain 
amount  of  waste  in  dung-making,  but  this  is  repaired 
by  the  growth  of  clover,  etc.,  and  by  the  purchase  of  a 
comparatively  limited  amount  of  fertilisers  or  feeding 
stuffs,  so  that  the  condition  of  the  land  is  maintained 
but  not  at  a  very  high  level.  Again,  at  the  other  end 
of  the  scale  we  have  the  intensive  farmer  who  uses 
his  land  as  a  sort  of  manufacturing  medium  to  convert 


xr.]       PLANT  FOOD  REMOVED  FROM  A  FARM       303 


fertilisers  into  crops,  and  steadily  increases  the  fertility 
of  his  soil  by  putting  on  more  plant  food  every  year 
than  he  removes  in  his  crops. 

We  can  begin  by  considering  what  is  necessary  to 
maintain  the  condition  of  the  land  under  a  conservative 
system  of  farming,  and  we  may  take  the  case  of  a  farm 
under  a  four-course  rotation,  where  nothing  but  corn 
and  meat  are  sold  and  all  the  dung  goes  back  to 
the  land.  Under  such  conditions,  as  we  have  already 
learnt,  the  feeding  animals  only  retain  about  10  per 
cent,  of  the  fertilising  constituents  of  the  food  they 
consume ;  the  other  90  per  cent,  comes  back  in  the 
manure  and  wholly  or  in  part  reaches  the  land  again. 

Table  LXXXVIII. — Fertilising  Constituents  removed  from 
Farm  in  Corn  and  Meat  Sold. 


Nitrogen. 

P2O5. 

K2O. 

Swede  Turnips,  20  tons  fed 
Barley,  6  quarters  sold         .... 
h  ton  Straw  fed,  the  rest  made  into  Dun;;-    , 
Clover,  2  tons  Hay  fed         .... 
Wheat,  4  quarters  sold         .... 
Straw  made  into  Dung. 

Total  for  4  acres         .        <> 

Per  acre  per  annum    . 

Lb. 

lO-O 

40-0 

1-2 

4-1 
35-2 

Lb. 

5-8 

180 

07 

2-8 

15-3 

Lb. 

0-7 

12-0 
O-I 

0-4 
10-3 

90-5 

42-6 

23-5 

22-6 

IO-6 

5-9 

In  this  way  the  land  loses  226  lb.  of  nitrogen  per 
acre  per  annum  ;  but  this  estimate  fails  to  take  into 
account  the  very  considerable  losses  that  occur  during 
the  making  of  the  farmyard  manure,  which  may  be 
estimated  at  50  lb.  in  the  four  years,  and  those  due  to 
drainage  and  bacterial  action.  On  the  other  hand,  the 
nitrogen  contained  in  the  clover  crop  has  been  obtained 


304  SYSTEMS  OF  MANURING  CROPS  [CHAP. 

from  the  atmosphere ;  indeed,  the  Rothamsted  experi- 
ments would  show  that  the  land  is  left  richer  in  nitrogen 
after  a  big  clover  crop  has  been  grown  and  taken  away. 
A  further  consideration  of  the  rotation  field  at 
Rothamsted  shows  that  the  clover  crop  alone  would  be 
able  to  maintain  the  fertility  of  the  land  at  about  the 
condition  which  would  produce  such  yields  as  are  shown 
in  the  table.  For  instance,  the  Agdell  field  in  the  47th 
to  the  50th  years  gave  the  following  crops  on  the  portion 
which  had  received  no  nitrogen  throughout  the  whole 
period,  though  phosphates  and  potash  are  supplied  to 
the  Swede  crop. 

Table  LXXXIX.— Produce  of  Agdell  Field  under  Rotation. 
No  Nitrogen  supplied  in  Manure.    (Rothamsted.) 


1894 

1895 
1896 
1897 


Clover  Hay 
Wheat 
Swedes 
Barley 


Carted  away       , 
Carted  away 
Consumed  on  the  land 
Carted  away 


64-7  cwts. 

r39-6  bushels,  and  25-3  cwts. 

\^     Straw. 

I2-0  tons. 

{37'7  bushels,  and  24-9  cwts. 
Straw. 


If,  then,  in  this  case  the  Swede  turnips  had  also 
received  whatever  manure  would  have  been  made  from 
the  clover  hay  and  the  wheat  and  barley  straw,  it  is 
evident  that  the  production  would  have  been  little  short 
of  the  average  indicated  in  Table  LXXXVIIL,  and 
that  the  nitrogen  necessary  to  maintain  the  fertility  of 
the  land  at  such  a  level  would  be  supplied  indefinitely 
by  the  recurring  clover  crop.  In  the  Agdell  example 
phosphatic  and  potassic  fertilisers  were  however  freely 
employed,  and  it  is  obvious  that  the  soil  possesses  no 
power  of  increasing  its  stock  of  these  constituents  in  the 
same  way  as  it  can  obtain  nitrogen  from  the  atmosphere. 
Three  hundred  and  fifty  pounds  of  superphosphate  per 
acre   during  the   four-year   period   of  rotation   would, 


XI.]         FERTILISERS  IN  ORDINARY  FARMING         305 

however,  repair  the  losses,  and  as  regards  potash  the 
losses  are  so  small  that  on  a  loamy  or  clay  soil  they 
would  be  made  up  by  the  continual  slow  weathering  into 
an  available  form  of  the  insoluble  potash  compounds  in 
the  soil. 

It  is,  however,  a  low  level  of  production  that  is 
attained  in  this  example  of  an  almost  self-supporting 
piece  of  land,  and  if  the  average  yield  is  to  be  raised, 
say  to  5  qrs.  of  wheat  and  6  qrs.  of  barley  per  acre,  an 
external  supply  of  nitrogen  must  be  obtained,  either  in 
the  form  of  fertilisers  or  feeding  stuffs.  Moreover,  this 
additional  nitrogen  must  be  considerably  more  than 
would  be  contained  in  the  extra  quarter  of  wheat  and 
other  larger  crops  that  are  grown  ;  there  must  be  enough 
to  compensate  for  the  greatly  increased  waste  by  drain- 
age, denitrification,  etc.,  which  will  accompany  the  higher 
fertility  of  the  soil.  Several  examples  have  already  been 
given  to  show  that  the  greater  the  amount  of  fertiliser 
added  to  the  soil  the  smaller  is  the  proportion  returned 
in  the  crop ;  these  are  only  particular  cases  of  the 
general  rule  that  the  wastage  of  nitrogen  is  greater 
the  higher  the  fertility  of  the  soil.  Fertilisers  go 
less  to  feed  the  crop  directly  than  to  maintain  the 
level  of  fertility  of  the  land,  and  as  this  rises  all  the 
actions  which  result  in  loss  of  nitrogen  are  increased 
at  a  rapid  rate.  Thus  the  intensive  farmer  often 
becomes  wasteful  because,  after  his  land  is  in  good 
heart,  he  continues  to  add  fertilisers  at  the  same  rate  as 
he  did  when  he  was  building  up  its  condition. 

It  therefore  follows  that  an  account  of  what  is 
removed  from  the  soil  year  by  year  by  the  crops  or 
animals  raised  upon  the  farm  provides  very  little 
guidance  towards  determining  the  amount  of  fertiliser 
which  must  be  brought  in ;  at  a  low  level  of  production, 
good  land  will  practically  recuperate  itself  without  any 

U 


3o6  SYSTEMS  OF  MANURING  CROPS         [chap. 

extraneous  manure,  while  really  high  farming  for  big 
crops  involves  a  considerable  wastage  of  nitrogen 
applied  to  the  land  and  never  recovered  in  the  crop.  It 
is  only  by  experience,  by  the  knowledge  of  his  own  land 
and  the  market  conditions  which  prevail,  that  the 
individual  farmer  can  tell  how  high  it  is  profitable  for 
him  to  farm,  and  therefore  to  what  degree  he  can 
utilise  the  information  as  to  feeding  his  crops  which  is 
provided  by  field  experiments. 

The  discussion  that  follows  of  the  manures  appropri- 
ate to  each  of  the  staple  crops  is  therefore  intended  to 
supply  the  farmer,  not  with  a  series  of  recipes  or  patent 
mixtures  that  are  universally  applicable,  but  with 
principles  out  of  which  he  can  construct  a  rational 
system  appropriate  to  his  own  farm.  In  the  practice  of 
farming  many  things  may  at  once  be  set  down  as 
"  wrong,"  but  there  can  be  nothing  absolutely  "  right " ; 
the  proper  course  of  action  is  never  anything  more  than 
a  judicious  compromise  adapted  to  all  the  various  con- 
ditions of  climate,  soil,  and  markets.  We  can  now 
consider  the  ordinary  farm  crops  separately. 

Wheat  in  the  typical  four-course  rotation  follows 
the  ploughed-up  clover  ley,  and  generally  derives  all 
the  nitrogen  it  requires  from  the  residues  left  by  the 
clover  in  the  soil.  In  many  cases,  however,  oats  are 
now  substituted  for  wheat  after  the  ley,  because  more 
time  is  thus  obtained  to  graze  the  aftermath  and 
break  up  the  land  before  seeding;  oats  also  after  the 
ploughed  land  has  been  exposed  for  the  winter  suffer 
less  than  wheat  from  the  wireworm  which  is  apt  to  be 
prevalent  in  the  old  clover  land.  Should  wheat  follow  a 
good  crop  of  clover  further  manuring  is  not  required ; 
though  if  the  second  growth  of  the  clover  has  been 
allowed  to  ripen  seed,  which  removes  a  large  proportion 
of  the  stored  up  nitrogen,  or  if  much  rye  grass  has  been 


.-ii.]  MANURES  FOR  WHEAT  307 

present  in  the  seeds  mixture  and  the  clover  has  failed 
somewhat,  it  may  be  desirable  to  enrich  the  ground  still 
further.  This  may  be  done  either  by  spreading  a  coat- 
ing of  dung  ( i  o  tons  per  acre)  on  the  clover  before  plough- 
ing, or  by  a  spring  top-dressing  of  i  to  li  cwts.  per  acre 
of  nitrate  of  soda  or  sulphate  of  ammonia,  preferably 
the  former  for  wheat.  When  wheat  follows  mangolds, 
as  is  not  unfrequently  the  case,  no  manure  is  likely  to 
be  required,  because  the  mangolds  will  have  received 
dung  and  will  have  been  frequently  cultivated.  Speak- 
ing generally  on  soils  in  good  heart  wheat  will  rarely 
require  manuring ;  at  any  rate,  it  will  be  wise  to  wait 
until  the  early  spring,  if  the  plant  then  appears  to  be 
growing  badly  or  losing  ground  a  top  dressing  of  nitrate 
of  soda  (i  to  1 1  cwts.  per  acre),  sulphate  of  ammonia 
(i  cwt.  per  acre),  or  soot  (20  bushels  per  acre)  will  do 
all  that  is  needful.  Soot  has  for  some  centuries  been 
employed  as  a  spring  top-dressing  for  wheat ;  besides 
the  nitrogen  it  supplies,  it  also  tends  to  preserve  the 
plant  from  the  attacks  of  the  small  slugs  and  snails 
which  are  so  active  at  that  time  of  year. 

Of  course,  when  wheat  and  other  cereals  are  grown 
continuously  on  the  same  land,  as  on  Mr  Prout's  farm 
at  Sawbridgeworth,  it  is  necessary  to  employ  a  more 
complete  fertiliser — 2  cwts.  per  acre  of  nitrate  of  soda  or 
sulphate  of  ammonia  will  be  required  as  a  spring  top- 
dressing,  and  3  cwts.  of  superphosphate  or  2  cwts.  of  basic 
slag,  according  to  the  amount  of  calcium  carbonate  in 
the  soil,  should  be  sown  before  the  seed.  Potash  would 
only  be  necessary  on  the  lighter  soils,  on  which  wheat 
is  not  likely  to  be  grown  continuously,  but  in  such  a 
case  3  cwts.  or  so  per  acre  of  kainit  would  be  desirable. 
Fertilisers  for  wheat  may  be  crude  salts,  like  nitrate  of 
soda  or  superphosphate ;  the  establishment  of  a  plant 
is  little  affected  by  the  amount  of  humus  in  the  soil  and 


3o8  SYSTEMS  OF  MANURING  CROPS  [chap. 

the  extra  price  of  organic  manures  like  the  guanos  will 
rarely  be  repaid  by  any  increased  yield. 

Barley  is  grown  under  two  very  different  conditions 
of  tilth.  In  the  first  place,  it  may  follow  wheat  and 
form  the  second  or  even  the  third  white  straw  crop  after 
roots  or  a  clover  ley;  in  the  Isle  of  Thanet  three,  four, 
or  even  five  barley  crops  may  be  taken  in  succession 
after  an  old  lucerne  or  sainfoin  ley  has  been  broken  up. 
In  such  cases  the  high  condition  will  have  been  taken 
out  of  the  soil  by  the  first  crop  of  wheat,  there  will  no 
longer  be  any  excess  of  readily  available  nitrogen,  and 
as  there  is  a  good  opportunity  of  getting  the  soil  early 
into  tilth,  barley  of  high  quality  may  be  expected. 
Good  malting  barley  contains  a  low  percentage  of 
nitrogen,  hence  the  soil  on  which  it  grows  must  not  be 
too  rich,  nor  must  any  large  quantity  of  nitrogenous 
manure  be  employed.  On  the  other  hand,  however,  it 
is  a  mistake  to  suppose  that  impoverished  soil  alone 
will  yield  good  barley ;  unless  a  reasonable  amount  of 
nitrogen  be  available  not  only  will  the  yield  be  small 
but  the  size  of  the  berry  will  fall  away.  This  may  be 
illustrated  from  the  Rothamsted  experiments  on  the 
Agdell  field,  where  the  barley  follows  Swede  turnips  in 
the  rotation.  On  this  field  the  plots  are  manured  for 
the  root  crop  but  not  for  the  barley  which  follows,  and 
on  three  of  the  plots  the  following  average  results  were 
obtained  (Table  XC). 

The  soil  of  the  first  plot  was  in  a  very  impoverished 
condition  because  a  crop  of  roots  had  been  grown 
without  nitrogenous  manure  and  had  been  wholly 
removed  from  the  soil ;  the  grain  in  consequence  was 
poorly  developed  for  want  of  nitrogen,  as  is  shown  by 
its  low  weight  per  bushel  and  per  looo  grains ;  its  value 
was,  in  consequence,  low  in  spite  of  the  small  percentage 
of  nitrogen  it  contained.     The  second  plot,  on  which  a 


XL] 


MANURES  FOR  BARLE  V 


309 


small  crop  of  roots  had  been  fed,  gave  the  best  results ; 
the  third  plot,  on  which  a  large  crop  of  roots  had  been 
fed,  evidently  received  too  much  nitrogen,  as  shown 
by  the  high  percentage  in  the  grain  ;  as  a  result  the 
value  fell  off.  The  figures  are  the  means  of  several 
years'  valuations. 

Table  XC— Relation  of  Quality  of  Barley  to  the  Nitrogen 
SUPPLIED  IN  Manure  (Rothamsted). 


Manuring 
for  Roots. 

Treatment 
of  Roots. 

Yield  of 
Barley, 
per  acre. 

(B.Q 

0. 

o.S  ™- 
•£0  w> 

9 '5 

ID   U 

i 

^.2 

Grain. 

Straw. 

Minerals,  no 

Bush. 

Cwts. 

Nitrogen  . 
Minerals,  no 

Carted  off    . 

13-6 

9.2 

54-0 

397 

1-484 

28/7 

Nitrogen  . 
Minerals  and 

Fed  on  Land 

28-9 

17-5 

55-3 

44-3 

1-576 

29/11 

Nitrogen  . 

Fed  on  Land 

34-1 

23-4 

55-3 

46-2 

1-693 

29/6 

In  preparing  for  a  crop  of  barley  of  high  quality  it 
is  therefore  necessary  not  to  allow  the  land  to  become 
really  poor,  but  it  is  desirable  that  the  nitrogen  should 
come  more  from  condition  in  the  land  than  from  very 
active  manures.  If  the  land  is  in  really  high  condition 
before  the  first  straw  crop  of  wheat  or  oats  is  taken, 
barley  may  follow  without  any  fertiliser,  especially 
if  the  ground  can  be  got  into  good  tilth  and  the 
barley  sown  really  early.  But  for  a  second  barley 
crop  or  for  the  first  on  land  in  poorer  heart  some 
nitrogenous  manure  must  be  used,  and  sulphate  of 
ammonia  and  rape  cake  are  found  to  give  better 
quality  than  nitrate  of  soda,  though  in  neither  case 
must  a  large  quantity  be  used.  Furthermore,  it  has 
been  shown  earlier  (p.  140)  that  phosphoric  acid  is  a  very 
essential   constituent   of  any   fertiliser  for  barley,  and 


3IO  SYSTEMS  OF  MANURING  CROPS         [chap. 

whatever  the  tilth  it  seems  desirable  to  give  this  crop 
about  3  cwts.  per  acre  of  superphosphate,  or  its  equivalent 
in  steamed  bone  flour  or  phosphatic  guano  on  light  soils 
poor  in  carbonate  of  lime.  The  question  of  potash  is 
more  doubtful ;  while  potash  manures  have  been  found 
to  stiffen  the  straw  and  increase  the  size  of  the  berry- 
by  promoting  starch-formation,  they  also  prolong  the 
maturity  of  the  barley  and  darken  its  colour  slightly. 
Hence,  potash  manures  must  be  used  carefully  and  are 
only  likely  to  be  valuable  on  light  sandy  or  gravelly 
soils.  We  thus  arrive  at  the  following  mixture  for  a 
barley  manure,  when  barley  follows  one  or  more  white 
straw  crops  and  the  land  is  no  longer  in  high  condi- 
tion : — 

Sulphate  of  ammonia  ^  to  i|  cwts.,  or  rape  dust  4  to 
6  cwts.  per  acre. 

Superphosphate  3  cwts.  per  acre,  or  steamed  bone 
flour  2  cwts. 

Sulphate  of  potash  \  cwt.  per  acre,  on  light  soils 
only. 

The  superphosphate  and  sulphate  of  ammonia  or 
rape  dust  should  be  mixed  and  sown  broadcast  before 
the  seed  is  drilled ;  it  is  impossible  to  distribute  small 
quantities  like  a  |  to  i  cwt.  as  a  top  dressing  evenly 
unless  they  are  mixed  with  a  much  larger  bulk  of 
ashes. 

A  mixture  of  this  kind  would  also  serve  for  the  rare 
case  of  barley  following  roots  which  have  been  grown 
without  farmyard  manure  and  then  carted  off  the  land. 

When  barley  follows  roots  which  have  been  highly 
manured  with  farmyard  manure,  still  more  so  when  the 
roots  have  been  folded  off  by  sheep,  the  land  is  already 
too  rich  in  readily  available  nitrogen  to  grow  barley  of 
the  highest  quality,  the  more  so  as  the  roots  are  often 
left  so  late  on  the  ground  that  a  good  seed-bed  cannot 


XI.]  MANURES  FOR  OATS  31 1 

be  obtained  early  in  the  year.  Early  sowing  is  essential 
for  barley  of  high  quality,  and  except  on  the  very 
lightest  soils  if  the  root  land  cannot  be  broken  up  before 
the  New  Year,  so  that  the  frosts  may  have  time  to  break 
down  the  clods  which  have  been  formed  by  the  sheep 
treading  the  wet  land,  it  is  better  to  sow  either  oats  or 
a  barley  like  Archer's,  which  will  yield  well  for  feeding 
purposes  though  the  quality  may  not  reach  a  malting 
standard.  When  the  roots  have  been  fed  on  the  land 
3  cwts.  per  acre  of  superphosphate  sown  with  the  seed  is 
found  to  improve  the  quality  of  the  grain  and  help  to 
correct  the  excess  of  nitrogen ;  but  neither  potash 
fertilisers  nor  salt,  which  is  sometimes  recommended 
and  which  acts  as  a  liberator  of  potash  in  the  soil,  are 
of  value  except  on  the  very  lightest  of  soils.  When  the 
roots  have  been  grown  with  farmyard  manure  and  then 
carted  off  the  land  will  be  in  about  the  right  condition 
for  barley,  and  will  want  no  help  except  a  little  super- 
phosphate, should  none  have  been  used  for  the  root  crop. 
Oats. — The  general  principles  of  manuring  for  barley 
hold  also  for  oats,  except  that,  being  grown  for  feeding 
purposes  only,  they  can  be  given  much  larger  quantities 
of  nitrogen  without  any  fear  of  injuring  their  quality. 
When  grown  on  a  ploughed-up  ley,  which  in  many  cases 
is  also  lightly  dunged  before  ploughing,  oats  are  not 
likely  to  require  any  fertiliser;  at  the  most  a  little 
nitrate  of  soda  if  they  are  found  to  be  starting  away  too 
slowly.  As  an  all-round  fertiliser  for  oats  when  the 
land  is  in  poor  condition  i  to  2  cwts.  of  nitrate  of  soda 
or  sulphate  of  ammonia,  and  2  cwts.  of  superphosphate 
or  basic  slag,  according  to  the  class  of  soil,  will  answer 
all  the  requirements  of  the  oat  crop ;  potash  fertilisers 
would  be  wasted,  as  also  would  the  more  expensive 
organic  forms  of  nitrogen  with  a  crop  which  occupies 
the  land  for  so  short  a  period.     Of  course,  in  a  wet 


312  SYSTEMS  OF  MANURING  CROPS  [chap. 

season  as  much  as  2  cwts.  per  acre  of  nitrogenous  manure 
might  easily  result  in  the  crop  going  down. 

Rye,  which  is  grown  in  the  south  of  England  for 
early  spring  keep  is  rarely  manured  ;  but  maize,  which  is 
also  grown  to  some  extent  as  fodder,  requires  the  land 
to  be  brought  into  fairly  high  condition.  A  preliminary 
dressing  of  12  to  15  loads  of  dung  per  acre  should  be 
given,  with  2  to  3  cwts.  per  acre  of  superphosphate  at 
the  time  of  sowing,  then  i  cwt.  per  acre  of  nitrate  of 
soda  may  be  used  as  a  top  dressing  round  the  plants 
when  they  are  set  out  and  side  hoed. 

Root-crops. — In  British  farming  the  bulk  of  the 
manure  that  is  made  upon  the  farm  or  purchased  is 
applied  to  the  root-crops — Swedes  or  mangolds  ;  though 
in  the  east  and  south-east  of  England  it  is  more  general 
to  apply  the  farmyard  manure  to  the  seeds  before 
ploughing  up  for  wheat.  In  these  warm  soils  much 
nitrogenous  manure  is  apt  to  cause  Swedes  to  run  to 
top  and  to  be  more  susceptible  to  mildew.  Big  crops 
of  roots  mean  more  food  for  the  stock,  and  so  in  turn 
more  farmyard  manure.  Moreover,  the  roots  are  grateful, 
and  continue  to  respond  to  liberal  treatment  without 
lodging  or  growing  an  excess  of  straw,  as  cereal  crops 
will  do.  It  is  questionable,  however,  whether  the  very 
common  practice  in  the  north  of  putting  on  all  the 
available  manure,  farmyard  and  artificial,  for  the  root- 
crop  and  making  that  serve  for  the  whole  of  the  rotation, 
is  wise ;  better  results  will  be  obtained  by  a  careful 
adaptation  of  the  fertiliser  to  the  particular  crops  form- 
ing the  rotation.  As  regards  Swedes,  the  earliest  work 
that  was  done  at  Rothamsted  consisted  in  showing  the 
dependence  of  this  crop  upon  an  ample  supply  of 
phosphatic  manure  of  an  available  character,  and  it  was 
the  response  of  this  crop  to  soluble  phosphates  which 
built  up  the  superphosphate  and  other  artificial  fertiliser 


XI.]  MANURES  FOR  SWEDES  313 

industries.  The  point  may  be  illustrated  from  the 
Rothamsted  experiments  on  the  Agdell  field,  where 
crops  are  grown  in  rotation  with  the  following  average 
results : — 

Unmanured 16  cwts. 

Mineral  only  —  Superphosphate  and 
Sulphate  of  Potash      .         .        ,        .       208     „ 

Complete  Manure  —  Nitrogen,  Super- 
phosphate, and  Sulphate  of  Potash    .       400    „ 

Without  manure  the  yield  is  trifling,  but  with  the 
mineral  manures  (and  the  phosphoric  acid  is  the 
effective  factor)  the  yield  rises  to  208  cwts.  per  acre, 
although  the  land  had  been  continually  cropped  without 
any  nitrogen  supply ;  lastly,  when  nitrogen  also  is 
added,  the  yield  becomes  that  of  a  high  average  crop 
for  the  south  of  England.  In  practice,  however,  it  is 
found  that  where  the  land  has  been  kept  in  good  con- 
dition and  there  has  been  adequate  preparation  of  the 
seed-bed,  little  or  no  manurial  nitrogen  will  be  required 
to  supplement  the  nitrates  produced  from  the  soil 
reserves,  and  that  consequently  the  great  increase  due 
to  the  nitrogen  in  the  experiments  quoted  will  not  be 
reproduced  under  ordinary  conditions  of  farming. 

In  a  large  co-operative  series  of  trials  undertaken 
by  the  Highland  and  Agricultural  Society  over  the 
whole  of  Scotland  it  was  found  that  84  lb.  per  acre  of 
sulphate  of  ammonia,  or  its  equivalent  in  i  cwt  of  nitrate 
of  soda,  was  as  much  nitrogenous  manure  as  could  be 
profitably  employed.  About  5  cwts.  per  acre  of  super- 
phosphate, or  4  cwts.  of  basic  slag,  or  2  cwts.  of  steamed 
bone  flour,  according  to  the  soil,  were  indispensable  ;  the 
superphosphate  being  best  on  loams  and  calcareous 
soils,  the  basic  slag  on  clays  and  peaty  land,  and  the 
steamed  bone  flour  on  sands  and  gravels. 


314 


SYSTEMS  OF  MANURING  CROPS         [chap. 


An  abstract  from  these  experiments  shows  the 
following  average  results  obtained  from  io8  plots 
during  the  years  1892-94: — 

Table  XCI. — Yield  of  Turnips  with  different  Fertilisers. 


Roots 
per  acre. 

Unmanured  .....,..«■ 

Tons. 
II-3 
17-9 
i8-9 
I9-I 
i8-4 
17-0 
19-2 
19-4 

Superphosphate  and  Basic  Slag  (7^  cwts.  only)  . 
Superphosphate  (6  cwts.),  Sulphate  of  Ammonia  (|)      . 
Superphosphate  (6  cwts.),  Nitrate  of  Soda  (i  cwt.) 
Basic  Slag  (9  cwts.),  Nitrate  of  Soda  (i  cwt.) 
Bone  Meal  (4  cwts.).  Nitrate  of  Soda  (J  cwt.) 
Superphosphate,  Basic  Slag,  Nitrate  of  Soda  (i  cwt.) 
Superphosphate,  Basic  Slag,  Nitrate  of  Soda  (2  cwts.) 

It  will  be  seen  that  in  these  experiments  the 
phosphatic  manures  are  the  most  effective  in  producing 
an  increased  yield ;  phosphate  alone  put  up  the  crop 
from  11-3  to  17-9  tons  per  acre:  i  cwt.  of  nitrate  of 
soda  or  sulphate  of  ammonia  only  add  about  another 
ton  to  the  crop,  while  a  second  hundredweight  produced 
no  perceptible  increase  at  all. 

The  question  of  the  most  appropriate  manurial 
treatment  for  Swedes  depends  upon  how  much  farmyard 
manure  is  available ;  while  the  ordinary  four-course 
rotation  is  being  practised,  most  of  the  dung  made  will 
come  back  to  the  land  for  the  Swede  crop,  about  10  tons 
to  the  acre  being  available.  Of  course,  with  such 
quantities  of  farmyard  manure  the  Swedes  will  require 
no  further  nitrogenous  dressing;  phosphates  are, however, 
still  indispensable.  In  such  cases  it  is  generally  the 
custom  to  finish  off  the  seed-bed  preparation  with  a 
ridging  plough,  and  to  apply  the  dung  to  the  furrows 
just  before  sowing.  The  ridges  are  then  split  back  over 
the  dung,  the  new  ridges  thus  formed  are  rolled,  and 


XI.]  MANURES  FOR  SWEDES  315 

the  seed  and  superphosphate  are  sown  from  the  same 
drill  on  the  top  of  the  ridge.  This  plan  answers 
excellently  in  the  cooler  and  moister  parts  of  the 
country,  where  the  Swede  flourishes  and  grows  big 
crops,  but  in  the  south  and  east  of  England  such  a 
method  exposes  the  crop  too  much  to  risk  of  damage 
from  drought,  both  through  evaporation  from  the  sides 
of  the  ridge  and  because  the  fresh  manure  as  it  rots 
leaves  the  land  too  open.  On  warm  dry  soils  it  is  better 
to  plough  in  the  farmyard  manure  in  the  autumn,  and 
to  sow  the  Swedes  on  the  flat  with  their  appropriate 
artificial  manure.  It  is  in  the  south  again  that  farm- 
yard manure  is  often  lacking  for  the  Swede  crop,  because 
it  has  been  wanted  for  wheat  or  hops  or  potatoes,  or 
sometimes  for  the  grass  land ;  many  sheep  farmers, 
again,  who  fold  on  the  Swede  land  have  a  strong 
objection  to  Swedes  grown  with  farmyard  manure.  A 
suitable  mixture  in  this  case,  when  no  farmyard  manure 
is  available,  will  consist  of  4  cwts,  of  superphosphate 
(or  its  equivalent  in  basic  slag  or  steamed  bone  flour 
as  before),  2  cwts.  of  fish  or  meat  guano,  and  \  cwt.  of 
a  mixture  of  nitrate  of  soda  and  sulphate  of  ammonia 
as  a  top  dressing  when  the  plants  are  singled.  If  the 
land  is  in  really  good  heart,  the  fish  guano  can  be 
omitted  or  reduced.  It  will  be  seen  that  various  com- 
pounds of  nitrogen  are  used  in  order  to  ensure  a  steady 
and  continuous  supply  of  nitrates  as  long  as  the  plant 
is  growing ;  the  mixture  of  sulphate  of  ammonia  and 
nitrate  of  soda  ensures  a  neutral  reaction  in  the  soil. 
Though  superphosphate  and  sulphate  of  ammonia  are,  on 
the  whole,  the  best  fertilisers  in  their  respective  classes 
for  Swedes,  they  must  be  employed  with  care  where 
there  is  little  lime  in  the  soil,  and  not  at  all  if  the  land 
is  known  to  be  subject  to  "  finger-and-toe."  Both  are 
acid  manures,  and  the  organism  causing  finger-and-toe 


3i6  SYSTEMS  OF  MANURING  CROPS  [chap. 

only  flourishes  in  an  acid  medium.  Potash  salts  are 
rarely  used  for  the  Swede  crop,  though,  like  other  root- 
crops  storing  up  a  good  deal  of  carbohydrate,  the  Swede 
will  respond  to  liberal  allowances  of  potash.  On  the 
lighter  soils,  when  farmyard  manure  is  only  scantily 
used,  it  is  undoubtedly  wise  to  apply  about  3  cwts.  of 
kainit  while  the  land  is  being  prepared  for  the  seed- 
bed. 

Of  the  other  crops  allied  to  Swedes,  white  turnips 
require  much  the  same  treatment,  except  that  the  fish 
guano  may  be  omitted  because  they  possess  a  shorter 
period  of  growth,  while  the  potash  is  more  necessary. 
Kohl  rabi  may  have  just  the  same  treatment  as  Swedes, 
as  may  thousand-headed  kale  and  cabbage,  with  the 
addition  of  more  nitrogen.  Cabbages  in  particular  will 
respond  to  enormous  quantities  of  nitrogen  ;  in  addition 
to  the  farmyard  manure  or  fish  guano  recommended 
for  the  Swedes,  up  to  3  cwts.  per  acre  of  the  mixture  of 
nitrate  of  soda  and  sulphate  of  ammonia  may  be  used 
in  two  or  three  top  dressings.  In  market  garden  work 
such  active  nitrogenous  manure  brings  the  cabbages 
earlier  to  cutting  and  renders  them  tenderer,  though 
they  are  reputed  in  consequence  not  to  travel  so  well  to 
distant  markets.  Stock  feeders  do  not  like  cabbages  or 
any  other  root  crop  grown  with  an  excessive  amount  of 
nitrogen,  especially  of  nitrate  of  soda ;  the  plant 
material  that  has  been  forced  in  this  fashion  becomes 
a  poor  or  even  a  harmful  food,  but  whether  this  is  due 
to  the  increased  amount  of  nitrates  in  the  plant  or  to 
other  compounds  of  nitrogen  is  as  yet  uncertain. 

Mangolds  are  often  described  as  heavy  feeders,  by 
which  we  may  understand  that  the  yield  will  go  on 
responding  to  very  large  additions  of  manure  rather 
than  that  the  crop  removes  a  specially  large  amount  of 
manurial  constituents  from  the  soil ;  a  fact  which  would 


XL] 


MANURES  FOR  MANGOLDS 


317 


not  be  apparent  in  the  succeeding  crops  but  could  only 
be  ascertained  by  analysis.  The  mangold  differs  entirely 
from  the  Swede  in  its  requirements.  In  the  first  place, 
it  will  give  returns  for  very  large  quantities  of  nitrogen ; 
secondly,  it  needs  much  potash  and  but  little  phosphoric 
acid  in  the  fertiliser.  The  Rothamsted  experiments  show 
that  mangolds  can  be  grown  successfully  for  very  many 
years  in  succession  upon  the  same  land  if  suitable 
fertilisers  are  provided.  The  only  difBculty  experienced 
lies  in  the  getting  of  a  plant  on  the  plots  where  the 
tilth  of  the  soil  has  been  injured  by  long-continued 
treatment  in  one  particular  direction. 

The  results  given  by  some  of  the  Rothamsted  plots 
are  set  out  in  Table  XCII. 


Table  XCII.— Average  Yield  of  Mangolds  (Rothamsted). 
32  Years,  i 876-1 907. 


Superphosphate. 

Dung. 

No 
Potash. 

Potash, 
etc. 

Alone. 

With 
Phosphate 
and  Potash. 

Rape  Cake  ==98  lb.  N. 
Nitrate  of  Soda  =  86  lb.  N. 
Ammonium  Salts  =  86  lb.  N . 

II-I 

iS-3 
7-5 

22-0 

l8-o 

15-2 

24-5 
25-9 
22.5 

25.7 
26-4 
24.0 

These  results  illustrate  the  following  points  in  the 
manuring  of  mangolds : — 

(i)  The  value  of  dung  and  of  organic  manures  like 
rape  cake,  which,  by  maintaining  a  good  texture  in  the 
soil,  ensure  a  plant  and  a  vigorous  start. 

(2)  The  value  of  an  addition  of  active  nitrogenous 
manures,  particularly  nitrate  of  soda,  even  when  dung 
is  also  used. 

(3)  The    importance    of    potash    salts   even   when 


3i8  SYSTEMS  OF  MANURING  CROPS  [chap. 

farmyard  manure  rich  in  potash  is  also  used.  The 
beneficial  effect  of  potash  salts  is,  however,  less  apparent 
when  nitrate  of  soda  is  employed  as  a  source  of  nitrogen, 
because  the  soda  attacks  and  renders  soluble  some  of 
the  reserves  of  potash  in  the  soil.  Potash  thus  becomes 
more  necessary  when  ammonium  salts  or  rape  cake 
form  the  source  of  nitrogen ;  but  in  any  case  it  is 
desirable  to  use  some  sodium  salt,  such  as  common  salt 
itself,  as  an  economiser  of  the  more  valuable  potash. 

(4)  That  with  proper  manuring  mangolds  can  be 
grown  year  after  year  on  the  same  land  without  any 
falling-off  in  yield  or  any  accumulation  of  disease.  It 
is  sometimes  convenient  to  keep  a  little  piece  of  land  near 
the  homestead  always  in  mangolds,  this  can  be  done 
for  a  long  time  in  perfect  safety  if  organic  manures  are 
employed  to  maintain  the  texture  of  the  soil. 

Coming  now  to  the  requirements  of  the  crop  in 
practice,  not  much  variation  will  be  required  because  of 
its  position  in  the  rotation,  since  mangolds  are  practically 
always  grown  on  a  stubble  with  the  land  in  compara- 
tively poor  condition.  The  basis  of  a  manure  for  man- 
golds should  be  dung ;  probably  there  is  no  crop  in  the 
rotation  to  which  farmyard  manure  can  be  better  applied 
than  to  mangolds.  When,  therefore,  the  mangolds  are 
grown  on  a  portion  of  the  root  breadth,  the  dung  should 
be  concentrated  on  this  part  of  the  field.  On  light 
soils  and  in  dry  climates  it  is  better  to  plough  in  the 
dung  in  the  autumn  and  grow  the  mangolds  on  the 
flat,  lest  the  fresh  manure  should  leave  the  soil  too  open 
and  let  in  the  drought,  but  on  heavier  land  and  where 
the  rainfall  is  greater  the  land  will  generally  be  laid  up 
in  ridges.  The  dung  should  be  spread  in  the  furrows ; 
the  artificial  manure,  other  than  nitrate  of  soda  or  other 
active  nitrogenous  manure,  should  be  sown  on  the 
dung  and  the  ridges  then  split  back  on  to  the  dung. 


XI.)  MANURES  FOR  POTATOES  31^ 

Supposing  20  loads  of  dung  per  acre  to  be  available  for 
the  crop,  the  supplementary  manure  should  consist  of 
3  to  5  cwts.  per  acre  of  kainit  (the  larger  quantity  on 
light  soils),  and  2  cwts.  of  fish  guano  or  kindred  fertiliser 
if  the  land  is  in  poor  heart  and  a  large  yield  wanted. 
Phosphates  in  many  cases,  as  at  Rothamsted,  are  not 
required  when  dung  is  used,  but  on  soils  where 
phosphates  are  specially  necessary,  as  on  many  of  the 
clay  soils  so  suited  to  the  mangold  crop,  it  will  be  well 
to  add  2  cwts.  of  superphosphate  to  the  mixture  when- 
ever the  fish  guano  is  omitted.  The  after-treatment 
will  consist  in  giving  top  dressings  of  a  mixture  of 
equal  weights  of  nitrate  of  soda  and  salt ;  about  3  cwts. 
of  the  mixture  at  singling  time,  and  perhaps  an  equal 
amount  a  few  weeks  later,  should  a  specially  heavy 
yield  be  aimed  at. 

Potatoes. — It  is  more  than  usually  difficult  to  lay  down 
general  rules  for  the  manuring  of  the  potato  crop,  so 
varied  are  the  tilths  upon  which  it  is  grown  and  so 
different  are  the  yields  that  are  aimed  at.  Potato 
growing  is  largely  carried  out  in  the  neighbourhood  of 
great  cities  where  dung  can  be  cheaply  obtained ;  in 
such  cases  the  farmer  will  often  crop  suitable  land  every 
other  year  with  potatoes,  taking  a  cereal  or  a  green 
crop  in  the  intervening  years.  On  the  other  hand  the 
farmer  who  does  not  make  a  speciality  of  potatoes  will 
simply  plant  them  on  a  portion  of  his  mangold  or 
Swede  land,  while  in  good  potato-growing  districts 
they  will  form  one  item  in  a  five-  or  six-year  rotation. 
In  the  Lothians,  for  example,  a  common  rotation  is  : — 


Turnips    " 

/  Turnips. 

Barley 
Clover 
Oats 

-     or     - 

Barley. 

Potatoes. 

Oats. 

Potatoes 

Clover. 

Wheat      , 

.  Potatoes. 

320  SYSTEMS  OF  MANURING  CROPS  [chap. 

In  both  these  cases  about  30  loads  of  farmyard 
manure  are  put  on  the  stubble  and  ploughed  in  the 
autumn  before  the  potatoes  are  grown,  artificial 
fertilisers  to  the  value  of  20s.  or  30s.  are  also  added  in 
the  spring. 

Another  rotation  in  the  Dunbar  country,  so  famous 
for  the  high  quality  of  its  potatoes,  avoids  the  use  of 
any  farmyard  manure  : — 

Swedes,  in  part  fed  on  the  land. 

Barley. 

Clover,  cut  for  hay. 

Clover,  grazed  with  cake  and  corn. 

Potatoes,  no  farmyard  manure. 

Oats. 

On  the  Lincolnshire  fen  soils  a  common  rotation  is 
as  follows : — 

Swedes  ^,  Potatoes  J,  with  farmyard  manure. 

Wheat. 

Seeds. 

Wheat. 

Oats. 

On  the  black  soils  of  Lancashire  a  common  rotation 
is : — 

Oats. 
Potatoes. 
Oats. 

Seeds,  farmyard  manure  being  used  in 
large  quantities. 

In  view  of  all  these  variations  in  practice  it  will  be 
best  to  discuss  a  few  general  principles  : — 

(i)  Potatoes  do  not  want  an  excess  of  nitrogenous 
manure,  because  it  renders  them  waxy  and  gives  them 
a  tendency  to  boil  a  bad  colour ;  it  also  makes  them 
susceptible  to  disease.     As  quality  is  so  important,  the 


XI.]  MANURES  FOR  POTATOES  321 

nitrogen    they  require   should    be   derived   more   from 
mellow  soil  in  high  condition  than  from  recent  manure. 

(2)  A  good  supply  of  phosphatic  manure  has  been 
shown  to  be  important. 

(3)  Potash  is  essential,  since  the  potato  is  a  starch- 
making  plant. 

(4)  Manures  setting  up  an  alkaline  reaction  should 
be  avoided,  since  they  facilitate  the  attack  of  Oospora 
scabies,  the  fungus  causing  potato  scab.  Hence  sulphate 
of  ammonia  should  be  preferred  to  nitrate  of  soda  for  a 
top  dressing  and  superphosphate  to  basic  slag;  lime 
also  should  not  be  used. 

As  regards  the  use  of  dung  it  has  been  repeatedly 
shown  that  a  better  return  is  obtained  by  using 
farmyard  manure  in  moderate  quantities  of  20 
loads  per  acre  or  so  and  supplemented  with  artificial 
manures,  than  by  spending  all  the  money  available  for 
manuring  upon  dung  alone.  On  any  but  the  heaviest 
soils  it  is  better  to  plough  in  the  farmyard  manure  in 
the  autumn  and  so  get  the  land  into  good  heart,  but  on 
the  close  badly  working  soils  it  is  an  advantage  to  the 
potato  plant  to  have  the  ground  left  a  little  hollow  by  the 
decay  of  the  farmyard  manure ;  on  such  soils,  therefore, 
the  dung  should  be  applied  in  the  drills  just  before 
planting.  The  mixture  of  artificials  should  either  be 
sown  broadcast  before  the  land  is  ridged  up  or  sown 
upon  the  farmyard  manure  in  the  drills  before  the 
ridges  are  split.  For  ordinary  cropping  a  mixture  of 
4  cwts.  per  acre  of  superphosphate,  i  cwt.  of  sulphate  of 
potash  and  i  cwt.  of  sulphate  of  ammonia  will  be  ample  ; 
when  extra  heavy  crops  are  aimed  at,  2  cwts.  or  so  of  a 
good  guano  may  be  added  to  the  mixture  already 
specified,  and  a  further  hundredweight  of  sulphate  of 
ammonia  may  be  applied  as  a  top  dressing  when  the 
haulm  is  beginning  to  appear. 

X 


322  SYSTEMS  OF  MANURING  CROPS  [chap. 

The  Leguminous  Crops. — It  has  already  been 
explained  that  the  leguminous  plants  are  able  to  obtain 
nitrogen  from  the  atmosphere  by  the  agency  of  the 
bacteria  in  their  nodules  and  can  in  this  way  satisfy 
their  requirements  for  nitrogen :  it  should,  however, 
not  be  forgotten  that  they  also  feed  upon  combined 
nitrogen  like  all  other  plants,  and  as  a  rule  derive  their 
nitrogen  both  from  the  air  and  from  the  soil.  To 
obtain  the  biggest  crops  rich  soil  and  certain  nitro- 
genous manures  are  necessary,  but  to  secure  the  greatest 
profit  out  of  a  leguminous  crop,  it  should  be  left  as 
far  as  possible  to  derive  its  nitrogen  from  the  atmo- 
sphere. All  leguminous  plants  are  particularly  sensitive 
to  any  trace  of  acidity  in  the  soil,  so  alkaline  fertilisers 
like  basic  slag  or  nitrate  of  soda  should  be  selected. 
Lime  is  also  desirable,  both  for  its  basic  properties  and 
as  a  liberator  of  insoluble  potash  in  the  soil,  because  all 
leguminous  crops  are  specially  dependent  upon  an 
abundant  supply  of  potash. 

Beans. — Beans  no  longer  play  the  important  part  in 
British  agriculture  that  they  once  possessed  ;  essentially 
a  heavy  land  crop,  the  cultivation  has  declined  since  so 
much  of  the  strong  clay  land  has  been  laid  down  to 
grass.  In  the  rotation  beans  generally  come  between 
two  white  straw  crops.  They  will  follow  oats  or  barley, 
for  example,  and  precede  wheat,  and  as  a  rule  they  do 
not  receive  any  manure.  A  little  farmyard  manure 
may  be  spread  on  the  stubble  before  it  is  ploughed, 
but  other  nitrogenous  manures  have  little  beneficial 
effect  upon  the  crop.  The  Rothamsted  experiments 
show  that  beans,  like  other  leguminous  plants,  respond 
chiefly  to  phosphates  and  potash,  to  the  latter  especially, 
and  are  able  to  derive  most  of  the  nitrogen  they  require 
from  the  atmosphere.  For  example,  the  average  results 
for  eight  years  at  Rothamsted  were — 


XI.]  BEANS  AND  CLOVER 

Table  XCIII. — Yield  of  Beans  at  Rothamsted, 
1847-1854. 


323 


Unmanured. 

Minerals 
only. 

Minerals 
and  Nitrogen. 

Corn 

1205  lb. 

1676  lb. 

1763  lb. 

More  recent  experiments  made  by  the  Highland  and 
Agricultural  Society,  and  others  in  Essex,  upon  beans 
under  ordinary  farming  conditions  confirm  these  results, 
showing  that  nitrogenous  manures  are  non-effective  but 
that  the  crop  responds  to  phosphates  and  potash.  Thus 
in  practice,  when  beans  are  being  grown  on  strong  land, 
we  may  reduce  the  manuring  to  3  or  4  cwts.  per  acre  of 
basic  slag,  any  other  expenditure  on  fertiliser  is  not 
likely  to  be  repaid  by  the  increase  in  the  crop. 

Clover. — Red  Clover  forms  perhaps  the  most 
important  crop  cultivated  by  the  farmer ;  not  only  does 
the  hay  furnish  a  particularly  valuable  fodder,  the 
nitrogen  in  which  is  largely  derived  from  the  atmo- 
sphere and  is  therefore  clear  gain  to  the  farm,  but  the 
nitrogen  left  behind  in  the  roots  and  stubble  also 
enriches  the  land  for  future  crops. 

Since  the  time  of  the  Romans  it  has  been  known  that 
the  wheat  is  most  luxuriant  where  the  clover  had  grown 
best  in  the  preceding  year ;  the  Rothamsted  experi- 
ments afford  some  interesting  examples  from  which  the 
gain  of  nitrogen  can  be  estimated.  One  example  of 
the  great  benefit  which  the  succeeding  crops  in  a 
rotation  derive  from  a  good  crop  of  clover,  although 
it  is  removed  from  the  land  as  hay,  has  already  been 
quoted  (Table  VIII.,  p.  33). 

Again,  in  1873  a  piece  of  land  in  Little  Hoos  field 
was  cropped,  part  with  barley  and  part  with  clover,  in 
1874  barley  was  taken  over  the  whole,  and  the  amount 


324 


SYSTEAIS  OF  MANURING  CROPS 


[chap. 


of  nitrogen   removed  in  the  crop  from  each  piece  of 
land  was  estimated  as  follows : — 


Table  XCIV.— Gain  of  Nitrogen  by  Clover  Crop, 
rothamsted. 


Lb.  of  Nitrogen  removed  per  acre 
in  the  Crop. 

1873  . 

1874  .     . 

Nitrogen  per  cent. 

in  Soil,  end  of  1873. 

Barley,  37-3 
Barley,  39-1 

Clover,  1 51 -3 
Barley,     69-4 

0-1416 

0-1566 

Thus,  although  151  lb.  per  acre  of  nitrogen  was 
removed  in  1873  from  the  clover  portion  of  the  field,  as 
compared  with  37  lb.  from  the  barley  portion,  the  former 
in  the  following  year  yielded  an  extra  20  bushels  of 
barley. 

As  to  the  manurial  treatment  of  clover,  it  is  difficult 
to  quote  very  extensive  experiments,  because  of  the 
failure  of  the  plant  which  takes  place  through  clover 
"  sickness."  On  the  best  clover  soils  in  this  country  it 
cannot  be  grown  more  frequently  than  once  in  four 
years,  and  more  often  once  in  seven  or  eight  years  only 
is  safe.  The  Rothamsted  experiments  all  go  to  show 
that  manuring  alone  will  not  keep  off  clover  sickness, 
though  it  was  found  possible  to  maintain  a  long  succes- 
sion of  clover  crops  on  a  small  patch  of  rich  garden  soil. 
Lime  and  potash  salts  are  helpful  but  cannot  be  trusted 
to  maintain  the  plant  in  health.  The  Rothamsted 
experiments,  however,  served  to  show  that  nitrogenous 
manures  have  little  effect  (indeed,  sulphate  of  ammonia 
may  be  harmful),  but  that  mineral  manures,  and  potash 
in  particular,  are  of  great  value.  Nitrate  of  soda  has 
sometimes  been  found  beneficial  to  st-'mu'ate  a  weakly 


XL]  BEANS  AND  CLOVER  325 

plant  in  the  sprinc;,  and  doubtless  the  soda  had  a  share 
in  this  result,  but  clover  so  forced  has  a  bad  effect  upon 
stock.  In  practice  clover  is  rarely  manured  ;  it  is  nearly 
always  sown  in  the  barley  crop,  and  is  then  left  to  the 
mineral  residues  from  the  preceding  root  crop  and  the 
nitrogen  it  can  gain  from  the  atmosphere ;  at  the  most, 
a  little  farmyard  manure  may  be  spread  during  the 
winter  and  is  valuable  as  affording  shelter  to  the  young 
plants.  If  plenty  of  phosphates  have  been  used  for  the 
Swede  and  barley  crops,  nothing  more  in  this  direction 
is  likely  to  be  required,  but  on  many  soils,  especially  of 
the  lighter  kind,  an  application  of  potash  during  the 
late  autumn  or  winter  after  the  clover  has  been  sown 
will  have  a  marked  effect  upon  the  yield  of  clover,  and 
the  cost  of  about  4  cwts.  of  kainit  per  acre  will  be  amply 
repaid. 

It  is  rarely  wise  to  attempt  to  manure  standing  clover 
for  a  second  year's  crop  ;  nitrogenous  fertilisers  are  not 
required,  and  the  potash  and  phosphates  hardly  have 
time  to  get  well  down  to  the  plants'  roots  in  the  time 
the  crop  still  occupies  the  ground.  A  thin  coating  of 
dung  in  the  winter  is  valuable  for  its  shelter,  and  if  the 
crop  must  be  forced  along,  then  in  the  winter  3  cwts.  of 
basic  slag  and  3  cwts.  of  kainit  may  be  sown  broadcast ; 
even  if  they  do  not  produce  much  immediate  return 
they  will  not  be  washed  away. 

Lucerne  and  Sainfoin. — The  principles  which  have 
been  laid  down  for  the  treatment  of  clover  apply  equally 
to  lucerne  and  sainfoin  {i.e.,  that  mineral  manures  should 
be  used,  and  that  only  the  young  plant  will  respond  to 
fertilisers),  but  since  these  crops  are  generally  sown  to 
stand  five  years  or  more,  it  is  wise  to  make  a  good 
preparation  of  the  soil  before  sowing.  As  a  rule,  they 
are  sown  in  barley  or  oats  and  about  5  cwts.  per  acre  of 
basic  slag  should  be  worked  into  the  soil  before  sowing 


326  SYSTEMS  OF  MANURING  CROPS  [chap. 

the  corn  crop.  The  potash  salts  (4  cwts.  per  acre  of 
kainit),  being  soluble,  can  be  kept  until  the  autumn  or 
winter.  Beyond  this  it  is  not  wise  to  use  fertilisers  on 
these  crops ;  a  little  nitrate  of  soda  may  serve  to  give 
the  young  plant  a  start  in  its  first  spring,  and  a  coat  of 
dung  is  often  valuable,  but  the  proper  way  to  regard 
lucerne  or  sainfoin  is  as  a  cheap  means  of  enriching  the 
land  with  a  minimum  of  expenditure. 

Vetches,  Trefoil,  Crimson  Clover,  and  similar  rapidly 
growing  leguminous  crops  are  usually  grown  as  catch 
crops  on  land  that  is  already  in  good  heart  and  do  not 
require  any  fertiliser.  Lupins  are  sometimes  grown  on 
poor  sandy  land  in  order  to  be  ploughed  in  as  green 
manure ;  in  such  a  case  the  preparation  of  the  land 
(supposing  it  to  be  poor  heathy  land  undergoing 
reclamation)  should  include  the  application  of  4  to  5 
cwts.  per  acre  of  basic  slag  and  3  to  4  cwts.  of  kainit  to 
supply  the  lupins  with  the  necessary  mineral  food,  for 
without  it  they  could  neither  gather  nitrogen  nor 
accumulate  humus  for  the  amelioration  of  the  soil. 

Grass  Land. — In  considering  the  effect  of  manures 
upon  the  grass  crop,  we  have  to  take  into  account  not 
only  the  weight  of  the  produce  but  the  character  and 
botanical  composition  of  the  herbage  that  ensues. 
Every  meadow  possesses  a  characteristic  vegetation 
made  up  of  various  species  of  grasses,  a  few  leguminous 
plants  like  white  and  red  clover,  bird's  foot  trefoil,  the 
yellow  vetchling,  etc.,  and  sundry  miscellaneous  species 
which  are,  in  the  main,  of  little  value  to  stock  and  may 
be  classed  as  weeds.  The  proportion  which  each  of 
these  species  contributes  to  the  herbage  represents  the 
degree  to  which  it  is  suited  by  the  various  conditions  of 
food,  water,  soil,  texture,  etc.,  which  prevail  in  that  field. 
A  strenuous  competition  is  going  on  between  the 
different   species,   each   of    which    is   endeavouring  to 


XI.]  MANURES  FOR  GRASS  LAND  327 

crowd  out  its  neighbours,  so  that  the  characteristic 
vegetation  of  the  field  represents  the  state  of  equili- 
brium which  has  been  attained  by  the  various  plants 
under  the  prevailing  conditions  of  soil  and  climate. 
The  physical  texture  of  the  soil  has  much  to  do  with 
the  nature  of  the  grasses  which  will  establish  themselves 
under  the  stress  of  competition  :  on  the  deep,  kindly 
alluvial  pastures  rye  grass  becomes  prominent ;  on  the 
thin  chalky  soils  of  the  Downs  sheep's  fescue  thrives 
best ;  on  heavy  clays  where  aeration  is  deficient  the 
creeping  rooted  bent  grass  will  cover  the  surface,  while 
sandy  droughty  soils  often  become  covered  with  tufts 
of  cock's  foot  or  brome  grass.  Just  in  the  same  way 
manuring,  by  altering  the  food  conditions  in  the  soil, 
can  effect  a  great  change  in  the  character  of  the  herbage 
of  a  given  field,  and  the  direction  which  these  changes 
will  take  must  be  kept  in  mind  in  any  discussion  of  the 
application  of  fertilisers  to  grass  land,  since  in  Great 
Britain  we  are  never  dealing  with  a  crop  of  a  pure 
unmixed  grass,  like  the  crops  of  timothy  or  blue-grass  in 
America.  The  best  example  of  the  effect  of  long- 
continued  manuring  on  the  composition  of  the  herbage 
is  afforded  by  the  Rothamsted  experiments,  where 
certain  plots  of  old  grass  land  receive  the  same  treat- 
ment every  year  and  are  mown  for  hay. 

Table  XCV.  shows  the  average  yield  for  fifty-three 
years,  and  also  the  character  of  the  resulting  herbage, 
as  shown  by  its  separation  into  grasses,  clovers,  and 
weeds  in  1902,  the  forty-seventh  year  of  the  experi- 
ment. 

From  this  table  certain  facts  become  apparent.  If 
grass  is  constantly  mown  without  any  return  in  manure, 
the  resulting  impoverishment  is  shown  not  only  in  the 
small  yield  but  in  the  preponderance  of  weeds  in  the 
herbage.       One  -  sided    manures,   which    contain   only 


328 


SYSTEMS  OF  MANURING  CROPS 


[chap. 


nitrogen  or  only  phosphoric  acid,  however  successful 
at  first,  eventually  result  in  increased  impoverishment 
of  the  land.  Nitrogenous  fertilisers  promote  the  growth 
of  the  grasses  at  the  expense  of  the  clovers.  Mineral 
manures,  and  particularly  potash,  promote  the  growth 
of  leguminous  plants  and  enable  them  to  make  headway 
against  the  grasses. 

Table  XCV.— Yield  and  Composition  of  Hay  at  Rothamsted. 


Botanical  Composition, 

Yield 

per  cent 

Plot. 

Manure. 

of 

ffi 

8 

Hay. 

c 

o 

a 

<s>  u 

a 

g 

+^t3 

2 

3 
1 

°o 

Cwts. 

3 

Unmanured 

21-5 

34-3 

7-5 

58-2 

I 

Nitrogen  only  as  Ammonium  Salts 

34-7 

77-6 

1-4 

2I-0 

17 

Nitrogen  only  as  Nitrate  of  Soda  . 

35-5 

43-8 

3-4 

52-9 

7 

Mineral  Manures,  no  Nitrogen 

40-9 

20-3 

55-3 

24-4 

4-2 

Phosphoric  Acid  and  Nitrogen,  no 

Potash       ..... 

35-8 

91-5 

8-5 

9 

Complete    Manure,   Nitrogen    as 

Ammonium  Salts 

54-8 

91-2 

1-3 

7-5 

H 

Complete    Manure,    Nitrogen   as 

Nitrate  of  Soda 

6o.8 

88-8 

3-7 

7-5 

ii-i 

Complete  Manure,  excess  of  Nitro- 

gen   

66-8 

99-2 

... 

0-8 

Another  consequence  follows  from  these  experi- 
ments ;  since  any  special  combination  of  fertilisers  or 
any  method  of  treatment  encourages  particular  species, 
the  best  results  in  any  given  field  will  always  be 
attained  by  persisting  in  the  treatment  selected.  For 
instance,  when  a  field  is  laid  up  for  hay  certain  strong- 
growing  grasses  get  an  advantage ;  when  the  field  is 
grazed  other  grasses  of  a  dwarfer-spreading  habit  are 
more  suited  by  the  conditions.  It  is  therefore  desirable 
to   keep  one  field  for  hay  every  year  and  another  for 


XI.]  MANURES  FOR  GRASS  LAND  329 

grazing,  rather  than  alternately  to  graze  and  hay  the 
same  field,  in  which  case  particular  grasses  are  first  of 
all  encouraged  and  then  repressed. 

Again,  we  may  conclude  that  manure  will  be  wasted 
upon  a  field  unless  there  is  a  proper  herbage  to  take 
advantage  of  it ;  in  dealing  with  poor  grass  land  it  is 
uneconomical  to  spend  much  on  manure  until  by 
degrees  the  character  of  the  vegetation  has  been 
reformed.  With  these  general  principles  in  mind,  we 
may  proceed  to  the  consideration  of  a  few  typical 
cases,  which,  however,  cannot  be  made  to  cover  all  the 
variations  of  soil  and  management  to  be  met  with  in 
practice. 

Land  laid  up  for  hay  every  year  must  receive  a 
regular  manuring,  unless  it  happens  to  be  rich  river 
meadow  or  alluvial  flat  which  derives  its  fertility  from 
the  percolating  water  or  the  mud  deposited  during  flood 
time.  But  if  it  is  ordinary  medium  grass  land,  about 
3  cwts.  per  acre  of  kainit  and  2  cwts.  of  superphosphate 
should  be  applied  in  the  early  spring,  in  January  or 
February,  followed  by  i  to  i|  cwts.  of  nitrate  of  soda  as 
soon  as  the  grass  begins  to  move.  On  heavy  soils, 
especially  on  old  grass  land,  basic  slag  may  be 
advantageously  substituted  for  the  superphosphate. 
At  intervals  of  five  years  or  so  the  mixture  of  artificial 
manures  should  be  replaced  by  a  winter  dressing  of 
15  tons  or  so  of  farmyard  manure.  Occasionally,  once 
in  five  or  six  years,  a  light  dressing  of  lime  should  be 
given,  a  ton  to  the  acre  put  on  in  the  form  of  ground 
quicklime  is  best.  Land  that  has  been  but  recently  laid 
down  to  grass  should  be  dunged  more  frequently.  If 
much  cake  and  corn  is  fed  on  the  aftermath  the  nitrate 
of  soda  can  be  reduced  or  even  omitted. 

Pasture  that  is  of  any  value  to  begin  with  will  rarely 
require  any  general  manuring,  so  much  cake  and  corn 


330  SYSTEMS  OF  MANURING  CROPS  [chap. 

will  usually  be  fed  to  the  stock  fattening  upon  it  in  the 
summer  that  as  regards  nitrogen  the  soil  is  likely  to 
become  richer  every  year.  Lime  and  phosphates  may, 
however,  often  be  deficient  on  these  rich  old  pastures, 
and  for  lack  of  these  constituents  the  great  residues  of 
manure  left  on  the  land  every  year  are  not  adequately 
realised.  For  this  reason  occasional  dressings  of  ground 
lime  (i  ton  per  acre)  and  of  basic  slag  (5  cwts.  per  acre) 
are  of  great  value  on  these  rich  lands  where  cake  and 
corn  are  fed.  The  result  of  the  application  may  not  be 
visible  in  an  increased  growth  of  grass,  but  the  cattle 
will  be  found  to  prefer  the  manured  portions  of  the  field 
and  to  thrive  there  better.  The  prevalence  of  weeds, 
especially  buttercups  and  to  a  less  degree  daisies,  is 
an  indication  of  this  over-richness  produced  by  heavy 
cake  feeding,  unconnected  by  an  adequate  supply  of 
minerals. 

Poor  pasture  cannot  repay  any  large  expenditure  ; 
indeed,  any  liberal  application  of  manures  at  first  will 
only  encourage  the  strongly  growing  weeds.  The  poor 
grass  land  in  Great  Britain  may  be  divided  into  three 
classes:  (i)  poor  clay  land  covered  with  creeping-rooted 
bent  grass ;  (2)  thin  sandy  soils  covered  with  sheep's 
fescue,  fiorin,  sweet  vernal,  and  soft  brome  grasses ; 
(3)  thin  soils  near  the  chalk  with  an  extremely 
variegated  herbage. 

As  regards  the  first  class  of  land,  the  experiments 
initiated  by  Somerville  at  Cockle  Park,  and  extended 
later  to  many  other  clay  soils  all  over  the  country, 
show  that  dung  and  other  nitrogenous  manures  are 
worse  than  useless  on  such  soils.  The  sound  way  of 
improvement  is  to  give  them  a  dressing  of  10  cwts.  or 
so  per  acre  of  basic  slag,  whereupon  the  white  clover, 
which  before  existed  as  tiny  plants  under  the  bents,  is 
favoured  and  becomes  prominent  in  the  herbage.     The 


XI.]  MANURES  FOR  GRASS  LAND  331 

grazing  is  at  once  improved,  and  as  the  nitrogen  con- 
sumed mostly  comes  back  to  the  grass,  a  permanent 
improvement  sets  in.  Should  white  clover  not  appear 
the  season  after  the  basic  slag  has  been  sown,  it  is 
possible  that  the  land  was  without  the  small  plants 
mentioned  above,  and  a  few  pounds  of  white  clover 
seed  should  be  sown  and  harrowed  in.  After  this  first 
dressing  of  basic  slag,  the  land  will  steadily  improve  for 
five  or  six  years,  after  which  time  a  fresh  application  of 
fertiliser  is  called  for.  By  this  time  the  soil  will  have 
gained  nitrogen  through  the  growth  of  the  white  clover, 
but  it  will  not  be  wise  to  trust  to  basic  slag  alone  for 
the  second  dressing,  since  the  land  will  have  lost  some 
of  the  potash  liberated  by  the  original  treatment  with 
basic  slag.  The  second  and  later  dressings  should 
therefore  be  accompanied  by  about  3  cwts.  per  acre  of 
kainit  to  keep  the  clover  vigorous ;  and  if  the  land  is 
ever  laid  up  for  hay,  it  will  be  necessary  to  use 
nitrogenous  fertilisers  pretty  freely.  As  long  as  a 
pasture  containing  a  good  proportion  of  white  clover 
is  only  grazed,  it  is  probable  that  the  nitrogen  content 
of  the  land  does  not  fall  off,  but  we  cannot  trust  to 
white  clover  to  make  good  the  large  removal  of  nitrogen 
in  a  hay  crop. 

The  thin  sandy  soils  are  more  difficult  to  improve 
than  the  clays ;  basic  slag  exerts  but  little  effect,  partly 
because  the  soil  is  too  dry  to  allow  it  to  act  very  freely, 
but  more  because  there  is  but  little  potash  in  the  soil 
to  be  liberated  by  the  action  of  the  lime  in  the  basic 
slaer.  Bone  meal  has  often  been  recommended  for  these 
soils,  remembering  the  improvement  which  bones  have 
effected  upon  the  Cheshire  pastures.  Bone  meal  is, 
however,  too  slow  in  its  action  to  be  profitable,  and  a 
phosphate  like  steamed  bone  flour  or  phosphatic  guano 
will  be  better.     About  2  to  3  cwts.  of  such  a  phosphate 


332  SYSTEMS  OF  MANURING  CROPS  [chap. 

and  an  equal  amount  of  kainit  forms  the  only  mixture 
which  will  improve  the  herbage  on  these  very  light  soils, 
but  even  then  the  change  will  be  slow  and  never  so 
pronounced  as  on  clay  land,  because  the  tufted  deep- 
rooting  grasses  which  prevail  are  better  able  to  resist 
the  competition  of  the  leguminous  plants.  Nitrogenous 
manures,  and  particularly  dung,  are  harmful  and  only 
encourage  the  coarse  herbage. 

On  the  thin  chalky  soils  nitrogenous  manures  are 
valuable,  and  a  pasture  may  be  permanently  improved 
as  well  as  enabled  to  carry  more  stock  in  the  current 
season  by  the  application  of  3  or  4  cwts.  per  acre  of  a 
mixed  fertiliser,  containing  3  of  superphosphate,  3  of 
kainit,  and  i  of  sulphate  of  ammonia.  But  for  the 
creation  of  a  good  pasture  on  the  thin  chalk  soils,  dung 
is  the  most  essential  manure  ;  as  much  farmyard  manure 
as  possible  should  be  spared  for  the  grass  land  and  a 
hay  crop  taken  the  season  after  the  application ;  then  it 
should  be  grazed  and,  if  necessary,  helped  during  the 
grazing  by  the  artificial  mixture  specified  above. 

But  it  must  always  be  remembered  that  on  the  thin 
dry  soils,  whether  chalk  or  sand,  only  a  very  limited 
expenditure  on  fertilisers  is  likely  to  be  repaid ;  large 
applications  of  manure  will  be  certainly  wasted,  but  it 
is  possible  gradually  to  build  up  better  pastures  by 
repeated  small  applications  of  the  nature  described. 

Seeds  hay  should  not  require  any  manuring ;  if  the 
land  has  been  properly  treated  before  the  seeds  were 
sown  there  should  be  enough  residue  from  previous 
manuring  to  grow  a  good  crop  of  mixed  seeds.  Any 
active  nitrogenous  manure  will  stimulate  the  rye  grass, 
etc.,  at  the  expense  of  the  more  valuable  clovers.  A 
fertiliser  is  sometimes  used  in  the  spring  when  the  land 
has  lost  plant  severely  through  the  winter,  but  this  is 
generally    a    wasteful    proceeding,    because    fertilisers 


XI.]  MANURES  FOR  HOPS  333 

should  only  be  used  when  there  is  a  crop  or  the  prospect 
of  a  crop  to  utih'se  them. 

When  land  has  been  newly  laid  down  to  grass,  there 
often  comes  a  very  critical  period  from  its  fourth  to  its 
seventh  year,  especially  on  stiff  soils  and  when  the  first 
two  or  three  crops  of  grass  have  been  fed  off  by  store  stock 
only.  At  that  period  the  leguminous  plants  have  begun 
to  die  away,  and  the  grasses  have  lost  vigour  because 
the  plant  food  that  had  been  rendered  available  by  the 
tillage  has  become  exhausted.  The  mechanical  con- 
dition of  the  soil  has  also  deteriorated  because  as  yet 
little  humus  has  been  accumulated.  Applications  of 
basic  slag  have  less  effect  than  usual  on  such  young 
grass  land,  there  are  no  residues  of  past  growth  to  be 
set  in  action  by  the  lime  of  the  basic  slag.  What  is 
wanted  is  either  farmyard  manure  or  applications  of  a 
complete  fertiliser  such  as  has  been  described  above. 
Better  still,  the  land  should  be  carefully  pastured,  the 
sheep  should  not  be  allowed  to  eat  too  closely,  and 
should  be  fed  with  cake  or  corn  to  enrich  the  land. 

Hops. — No  other  crop  is  so  liberally  manured  as 
hops ;  potato  land  may  perhaps  receive  as  much  in  any 
one  year,  but  on  hops  the  expenditure  for  fertilisers  will 
average  ^8  or  ;^io  per  acre  year  after  year.  The  hop 
plant  shows  no  special  requirements,  so  that  it  is  the 
needs  of  the  soil  rather  than  the  crop  which  should 
determine  variations  in  the  character  of  the  manure. 
The  manurial  treatment  of  hops  should  begin  with  a 
liberal  use  of  dung,  and  most  hop  growers  either  buy 
it  in  quantities  from  London  or  other  large  towns,  or 
fatten  cattle  or  pigs  in  order  to  make  enough  for  their 
requirements.  As  much  as  40  tons  per  acre  are  some- 
times employed  and  that  year  after  year,  but  one  such 
application  every  third  year  will  be  sufficient  to  maintain 
the  requisite  soil  texture,  and  in  the  intervening  years 


334  'SYSTEMS  OF  MANURING  CROPS  [chap. 

the  necessary  plant  food  can  be  more  cheaply  obtained 
in  other  forms.  The  subsidiary  manures  for  hops  are 
of  the  most  varied  nature,  but  shoddy  in  some  form  or 
other  is  a  highly  favoured  substance,  and  should  be 
applied  at  the  rate  of  from  i  to  2  tons  per  acre,  accord- 
ing to  its  richness  in  nitrogen,  in  the  autumns  when 
dung  is  not  being  used.  When  the  ground  is  first 
worked  in  the  spring  the  more  active  fertilisers  should 
be  applied,  6  cwts.  per  acre  of  fish  or  meat  guano  or  of 
rape  dust,  with  about  4  cwts.  per  acre  of  superphosphate, 
or  3  cwts,  of  steamed  bone  flour  or  phosphatic  guano, 
will  then  carry  the  crop  through.  Many  growers  are 
in  the  habit  of  using  a  further  dressing  of  rich  guano 
or  active  nitrogenous  manure  when  the  hops  are  coming 
into  burr,  but  this  is  probably  unwise,  as  it  induces  late 
sappy  growth,  very  susceptible  to  attacks  of  blight.  A 
good  coat  of  dung  at  this  time  is,  however,  of  great 
value,  especially  on  young  hops,  but  its  immediate  action 
is  more  as  a  mulch  than  a  fertiliser.  Potash  manures 
are  only  required  on  the  light  sandy  or  chalky  lands  ;  in 
such  cases  they  should  be  applied  in  the  winter  or  early 
spring.  Phosphates  are,  however,  most  essential ;  on 
the  strong  soils  as  much  as  10  cwts.  per  acre  of  basic 
slag  may  be  applied  in  the  winter  in  place  of  the  super- 
phosphate specified  above. 

Fruit plmiiations  under  tillage  should  receive  much 
the  same  kind  of  manuring  as  hops  do,  though  in  smaller 
quantities.  Dung  is  not  so  desirable,  and  the  necessary 
nitrogen  can  be  well  supplied  by  digging  in  i  ton  per 
acre  of  shoddy  in  the  winter,  or  a  spring  manuring  of 
meat  or  fish  guano  or  rape  dust  may  take  its  place. 
Phosphates  are  very  important,  and  potash  is  also 
indispensable,  especially  on  the  lighter  soils  and  for  all 
stone  fruit.  Four  cwts.  of  kainit  per  acre  may  be  given 
in   the  winter.     Fruit   trees   in  grass  land  should  not 


XI.]  MANURES  FOR  TROPICAL  CROPS  335 

receive  any  fertiliser,  but  should  be  manured  by  keep- 
ing the  land  closely  grazed  with  sheep  receiving  hay 
roots,  cake,  and  corn,  etc. 

Tropical  and  sub-tropical  crops. — It  is  very  difficult  to 
lay  down  any  general  rules  for  the  manuring  of  tropical 
and  sub-tropical  crops,  because  the  conditions  of  soil 
and  climate  are  subject  to  such  extreme  variations  that 
entirely  different  methods  of  treatment  have  to  be 
pursued  in  different  countries.  Certain  general  prin- 
ciples may,  however,  be  indicated,  to  be  taken  into 
account  whenever  any  scheme  of  manuring  has  to  be 
tentatively  adopted  in  practice.  All  the  processes  by 
which  the  insoluble  constituents  of  plant  food  in  the  soil 
are  rendered  available  for  the  plant  are  greatly  acceler- 
ated in  tropical  soils,  always  provided  they  contain  a 
sufficiency  of  water.  The  decay  of  organic  matter  takes 
place  with  extreme  rapidity,  so  that  the  humus  content 
of  cultivated  soils  will  be  quickly  reduced  unless  means 
are  found  of  repairing  the  losses  ;  for  the  same  reason 
all  organic  manures  containing  nitrogen  are  both  more 
quickly  and  more  completely  utilised  by  the  plant  than 
they  are  in  temperate  soils.  The  higher  temperature  of 
the  soil  water,  the  greater  production  of  carbon  dioxide 
in  the  soil,  also  result  in  a  more  rapid  weathering  of  the 
mineral  constituents  of  the  soil,  so  that  the  reserves  of 
phosphoric  acid  and  nitrogen  present  in  the  soil  are 
more  available  in  tropical  countries. 

It  also  follows  that  smaller  amounts  of  manure  in 
proportion  to  the  plant  food  withdrawn  by  the  crop  are 
effective  under  tropical  conditions  ;  whereas,  in  England, 
one  cannot  hope  to  recover  more  than  one-half  of  the 
nitrogen  applied  as  farmyard  manure,  in  a  hot  soil  with 
an  abundant  rainfall  nearly  the  whole  will  be  available, 
and  a  correspondingly  smaller  application  will  be 
required.     It  is  always  the  crops  of  short  duration  on 


336  SYSTEMS  OF  MANURING  CROPS  [chap. 

the  land — tobacco,  cotton,  and  to  a  less  extent  sugar 
cane — which  most  require  manuring ;  really  perennial 
crops  like  tea  and  coffee  require  much  less  manure  and 
that  of  a  more  slowly  acting  kind.  It  is  only  the  short- 
period  crops  which  will  respond  properly  to  active 
sources  of  nitrogen  like  nitrate  of  soda  or  sulphate  of 
ammonia. 

The  incidence  of  rainfall  must  be  closely  studied. 
No  manure  can  be  effective  when  the  soil  is  either  dry 
or  waterlogged ;  and  as  the  nitrogenous  manures  cannot 
be  expected  to  persist  very  long  in  the  soil,  their  applica- 
tion should  be  timed  so  as  to  be  followed  by  a  period  of 
growth  with  neither  excessive  rain  nor  a  dry  soil. 

Sugar  cane. — A  large  number  of  experiments  have 
been  conducted  with  sugar  cane,  and,  though  the  results 
naturally  vary  in  the  different  countries,  certain  general 
conclusions  can  be  drawn.  Before  planting,  a  compara- 
tively slow  acting  nitrogenous  fertiliser  should  be  used, 
either  the  equivalent  of  farmyard  manure  or  some  seed 
residue  like  castor  pomace,  to  supply  about  lOO  lb.  of 
nitrogen  per  acre.  For  the  rattoon  growths  more  active 
forms  of  nitrogen  are  desirable — either  sulphate  of 
ammonia  or  nitrate  of  soda  supplying  50  lb.  of  nitrogen 
per  acre ;  which  of  the  two  will  prove  the  more  suitable 
depends  upon  the  soil.  Excess  of  nitrogen  must  be 
avoided,  as  it  induces  late  cane  and  an  impure  juice. 
On  many  soils  applications  of  potash  salts  (sulphate 
of  potash  is  generally  the  most  economical  form)  are 
very  effective.  Phosphates  are  less  needed,  though 
superphosphate  is  often  valuable  on  black  alluvial  soils. 

Cotton. — Cotton  responds  freely  to  fertilisers,  and 
there  is  evidence  that  the  fertiliser  should  be  a  mixed 
one  but  mainly  phosphatic.  About  4  cwts.  per  acre 
of  superphosphate  and  2  cwts.  per  acre  of  cotton 
seed    meal    or    some    equivalent    organic     source     of 


XI.]  MANURES  FOR  TOBACCO  AND  TEA  337 

nitrogen,  should  be  ploughed  in  before  sowing,  and  this 
may  be  followed  up  by  a  ^  cwt.  per  acre  of  a  more 
active  nitrogenous  fertiliser  like  sulphate  of  ammonia  or 
nitrate  of  soda  when  the  crop  has  begun  to  grow. 
Potash  manures  are  only  required  on  certain  soils  of  a 
light  type. 

Tobacco. — Tobacco  is  a  crop  requiring  comparatively 
rich  land,  and  the  fertilisers  should  chiefly  supply 
nitrogen  and  potash,  phosphates  being  less  required. 
Too  great  an  amount  of  nitrogenous  fertiliser  should  not 
be  used,  or  the  quality  of  the  leaf  falls  off,  up  to  50  lb. 
per  acre  is  safe ;  and  ammoniacal  manures  should  be 
avoided,  as  they  result  in  a  leaf  burning  badly.  Before 
planting  out  the  tobacco  200  to  300  lb.  of  an  organic 
nitrogen  compound — cotton  seed  meal  or  castor  pomace 
— 200  lb.  of  superphosphate  and  100  lb.  of  sulphate  of 
potash  should  be  applied,  followed  by  100  lb.  of  nitrate 
of  soda  when  the  plant  is  growing.  Potash  appears  to 
be  very  essential,  and  may  be  given  as  nitrate,  carbonate, 
or  sulphate. 

Tea. — Being  perennial  the  tea  plant  requires  neither 
heavy  nor  active  manuring ;  it  is  also  very  important  to 
maintain  both  the  proper  habit  of  growth  of  the  plant 
and  the  quality  of  the  leaf.  If  any  large  amount  of 
nitrogen  is  employed  an  excessive  development  of  weak 
vegetative  shoots  takes  place  on  the  bush,  and  the  plant 
suffers  in  ensuing  seasons.  The  fertility  of  a  tea  garden 
as  regards  nitrogen  can  be  maintained  by  carefully 
burying  the  lighter  prunings  and  weeds,  and  by  digging 
in  from  time  to  time  leguminous  plants  which  have  been 
grown  between  the  rows,  cut  down,  and  allowed  to 
wither  and  rot  somewhat.  By  also  supplying  basic  slag 
at  the  rate  of  about  2  cwts.  per  acre  the  residues  thus 
utilised  are  balanced  by  the  phosphates,  and  the  lime  of 
the  basic  slag  is  beneficial  in  keeping  the  soil  healthy 

Y 


338  SYSTEMS  OF  MANURING  CROPS         [chap. 

and  in  assisting  the  decay  of  the  organic  matter.  When 
manures  are  necessary  it  is  best  to  employ  slow  acting 
substances  like  bone  meal  and  castor  pomace. 

Garden  manures. — In  an  ordinary  way  gardens 
require  little  artificial  fertiliser,  since  they  receive  a 
superabundance  of  stable  manure  until  the  soil  often 
becomes  over-rich  in  nitrogenous  residues.  Under  such 
conditions  the  only  fertiliser  wanted  will  be  some  form 
of  phosphatic  manure,  and  this  is  very  desirable  to 
induce  a  properly  balanced  growth  in  the  crops.  Super- 
phosphate may  be  used  on  the  loams,  basic  slag  on  the 
strong  soils,  steamed  bone  flour  or  phosphatic  guano 
when  the  soil  is  sand  or  gravel,  and  about  \  lb.  per 
square  yard  of  one  of  these  fertilisers  should  be  dug 
in  with  the  farmyard  manure  on  those  portions  of 
the  ground  which  come  to  be  dunged  in  the  usual 
rotation.  Nitrate  of  soda  is  often  valuable  to  push 
on  early  lettuce,  cabbage,  peas,  etc.,  in  a  backward 
spring;  it  may  also  be  applied  with  advantage  to 
asparagus  and  celery.  The  compound  garden  man- 
ures sold  under  fancy  prices  should  be  avoided : 
though  good  fertilisers  enough,  their  cost  is  exces- 
sive, even  considering  the  small  parcels  in  which 
they  are  sold.  Where  stable  manure  is  not  available 
and  a  mixed  fertiliser  is  required,  nothing  is  better 
than  a  good  Peruvian  guano  with  6  or  7  per  cent. 
of  nitrogen.  In  such  circumstances  the  humus  of  the 
soil  should  be  maintained  by  digging  in  as  much  organic 
matter — weeds,  grass  clippings,  vegetable  refuse,  etc. — 
as  possible,  and  by  growing  mustard  on  any  land  that  is 
not  wanted  for  a  short  time,  and  digging  the  green  crop  in. 
It  should  not  be  forgotten  that  lawns  which  are  con- 
stantly cut  must  become  greatly  impoverished  if  they 
are  not  manured,  for  which  purpose  Peruvian  guano  at 
the  rate  of  2  oz.  per  square  yard  every  other  year  forms 


XI.]  MANURES  FOR  TOBACCO  AND  TEA  339 

a  suitable  dressing.  When  Peruvian  guano  or  any 
similar  concentrated  fertiliser  is  used  to  enrich  potting 
soil,  the  mixture  should  be  allowed  to  stand  a  week 
before  potting,  because  guano  and  all  kindred  manures, 
when  in  a  raw  condition,  are  very  destructive  of  young 
plant  roots. 


CHAPTER  XII 

THE    VALUATION    AND    PURCHASE    OF 
FERTILISERS 

Valuation  on  the  Unit  System — The  current  Market  Price  of  the 
Unit  of  Nitrogen,  Phosphate  of  Lime  and  Potash — Variations 
in  Unit  Values  due  to  Market  Fluctuations — Valuation  of 
Fertilisers  before  Purchase — The  Fertilisers  and  Feeding 
Stuffs  Act ;  Obligations  of  the  Vendor — Sampling  Consign- 
ments of  Fertilisers — Mixed  v.  Unmixed  Fertilisers — Incom- 
patibles — Residues  of  Fertilisers  after  the  Growth  of  one  or 
more  Crops  —  Valuation  of  unexhausted  Residues  derived 
from  the  Consumption  of  purchased  Feeding  Stuffs. 

In  buying  fertilisers  the  farmer  will  generally  have  a 
considerable  choice  between  materials  of  different  origin 
and  composition,  but  which  will  so  far  serve  the  same 
purpose  that  their  relative  price  becomes  the  most 
important  factor  in  determining  the  purchase  of  one  or 
the  other.  For  example,  should  an  active  nitrogenous 
manure  be  needed,  for  many  soils  and  crops  it  is  a 
matter  of  indifference  whether  nitrate  of  soda  or 
sulphate  of  ammonia  is  used ;  among  phosphatic 
manures  the  choice  may  be  between  superphosphate, 
basic  slag,  and  a  neutral  manure  like  steamed  bone 
flour ;  or,  to  take  a  case  where  even  fewer  secondary 
considerations  enter,  practically  nothing  but  relative 
cheapness  need  determine  a  decision  between  such 
materials  as  fish  and  meat  guanos  or  rape  cake.     But 

810 


CHAP.  XII.]      VALUATION  OF  FERTILISERS  341 

since  all  these  materials  possess  different  compositions, 
a  method  of  valuation  must  be  found  which  will  reduce 
them  to  a  common  basis  of  the  cost  of  the  actual 
fertilising  ingredients  alone — i.e.^  of  the  nitrogen,  the 
phosphoric  acid,  and  the  potash  respectively.  It  is 
possible,  for  example,  to  calculate  the  price  per  pound 
of  each  of  these  fundamental  substances,  but  the  more 
convenient  method  is  to  ascertain  the  cost  of  a  unit 
consisting  of  one-hundredth  of  a  ton ;  such  unit  cost 
being  obtained  by  dividing  the  price  per  ton  of  the 
fertiliser  by  the  percentage  of  the  constituent  in 
question. 

It  is  the  custom  of  merchants  to  set  out  the 
analysis  of  the  various  fertilisers  in  terms  of  both 
nitrogen  and  ammonia,  and  to  express  the  phosphatic 
constituents  sometimes  as  phosphoric  acid  but  more 
commonly  as  tri-calcium  phosphate,  and  again  to  give 
the  potassium  in  terms  of  potash,  whatever  may  happen 
to  be  the  form  in  which  the  element  is  actually  com- 
bined. For  example,  nitrate  of  soda  contains  no 
ammonia,  and  the  statement  that  a  given  sample  of 
nitrate  of  soda  contains  19  per  cent,  of  ammonia  is  only 
meant  to  signify  that  the  15-5  per  cent,  of  nitrogen 
present  is  equivalent  to  19  per  cent,  of  ammonia.  In 
superphosphate  the  phosphoric  acid  is  chiefly  combined 
as  di-hydrogen  calcium  phosphate,  CaH^PgOg,  hence 
an  analysis  setting  out  the  presence  of  26  per  cent,  of 
soluble  phosphate  or  of  tri-calcium  phosphate  rendered 
soluble,  must  be  read  as  meaning  that  it  contains  11-9 
per  cent,  of  phosphoric  acid  soluble  in  water,  which 
amount  of  phosphoric  acid  would  be  also  contained  in 
26  per  cent,  of  tri-calcium  phosphate.  Similarly,  muriate 
of  potash,  which  is  potassium  chloride — KCl — might  be 
described  as  containing  50  per  cent,  of  potash — K2O — 
though  no  true  potash  or  potassium  oxide  is  present ; 


342 


VALUATION  AND  PURCHASE 


[chap. 


the  statement  merely  signifies  that  the  essential 
element,  potassium,  is  present  in  such  a  quantity  that 
if  it  were  combined  with  oxygen  as  potash  the  latter 
would  amount  to  50  per  cent,  of  the  fertiliser.  It  is 
therefore  necessary  to  remember  that  14  of  nitrogen 
are  equivalent  to  17  of  ammonia,  and  that  142  of 
phosphoric  acid  are  contained  in  310  of  tri-calcium 
phosphate  (see  p.  377),  but  that  necessity  of  making 
such  calculations  is  obviated  by  the  fact  that  in  the 
United  Kingdom  dealers  in  fertilisers  are  now  obliged 
to  give  the  analysis  of  their  wares  in  terms  of  nitrogen, 
tri-calcium  phosphate,  and  potash,  on  which  basis  the 
calculations  which  follow  will  be  made. 

The  prices  given  are  the  wholesale  prices  ruling  in 
London  in  October  1908;  naturally  they  do  not  hold  for 
other  times  and  places,  and  they  do  not  include 
carriage,  but  they  are  comparable  among  themselves 
and  with  due  additions  for  the  locality  show  the  range 
of  prices  which  may  be  expected  at  the  present  time. 

In  order  to  find  the  price  of  nitrogen,  we  can  take 
nitrate  of  soda  and  sulphate  of  ammonia,  which  contain 
nitrogen  only,  and  calculate  the  unit  value  as  follows : — 

Table  XCVI. — Price  of  Unit  of  Nitrogen. 


Price  per  ton. 

Nitrogen, 
per  cent. 

Unit- value 
of  Nitrogen. 

Sulphate  of  Ammonia    . 
Nitrate  of  Soda     . 

/ll,  15s. 
£10 

19-75  to  20-0 
I5-0     „   15-5 

I2S. 

13s. 

In  making  this  calculation  the  farmer  must  be 
careful  to  base  it  upon  the  price  per  ton  delivered 
at  his  local  station,  since  freight  charges  fall  more 
heavily  on  the  less  concentrated  manures,  to  such  an 
extent  indeed  that  at  distant  points  the  relative  cost 


XII.] 


UNIT  VALUES 


343 


of  different  fertilisers  may  be  entirely  altered  by  the 
carriage  charges.  In  the  instances  quoted  above  the 
two  fertilisers  contain  nitrogen  only  and  the  calculation 
is  consequently  of  the  simplest ;  as  a  rule,  however,  more 
than  one  constituent  is  present  The  unit  values  of 
the  two  have  to  be  obtained  by  a  little  adjustment  and 
do  not  possess  quite  the  arithmetical  certainty  which 
characterises  the  single  constituent  fertilisers.  Among 
phosphatic  fertilisers  there  are  practically  only  three 
which  contain  no  other  constituent,  and  in  these  the 
unit  value  of  tri-calcium  phosphate  may  be  calculated  as 
follows : — 

Table  XCVII.— Price  of  Unit  of  Phosphate  of  Lime. 


Tri-calcium 

Phosphate, 

per  cent. 

Price 
per  ton. 

Unit-value 

of  Tri-calcium 

Phosphate. 

Superphosphate,  high  grade 
Superphosphate,  low  grade 

Basic  Slagjg] ;        ;        ; 

Basic  Superphosphate 

35 

26 
38 

35 
25 

66s. 
50s. 
48s. 

45s. 
52s. 

IS.   lid. 
IS.   lid. 
IS.  3d. 
IS.  3d. 
2S.    Id. 

The  unit  is  dearer  in  the  superphosphates  because 
acid  has  been  employed  to  render  them  soluble  in  water. 

Supposing  it  is  now  desired  to  find  the  value  of  the 
phosphate  unit  in  certain  other  fertilisers  which  also 
contain  a  little  nitrogen,  it  is  necessary  to  make  a 
deduction  from  the  price  of  the  fertiliser  for  the 
nitrogen  present,  assuming  this  latter  to  have  approxi- 
mately the  value  calculated  from  such  purely  nitrogenous 
fertilisers  as  the  nitrate  of  soda  already  quoted.  For 
example,  steamed  bone  flour  containing  1-25  per  cent, 
nitrogen  and  59  per  cent,  tri-calcium  phosphate  is  quoted 
at  £\,  7s.  6d.  per  ton;  taking  nitrogen  at  13s.  per  unit 
the    1-25    per   cent,    would   be   worth    i6s.    3d.,  which 


344 


VALUATION  AND  PURCHASE 


[chap. 


deducted  from  ;^4,  7s.  6d.  leaves  ;^3,  lis.  3d.  for  the 
phosphate.  Dividing  this  figure  by  59  (the  percentage 
of  phosphate),  we  get  is.  2|d.  as  the  price  of  the  unit  of 
phosphate  of  lime. 

Calculating  in  this  way,  the  following  figures  are 
obtained  for  phosphatic  manures  containing  some 
nitrogen : — 


Table  XCVIIL- 

-Price  of  Unit 

OF  Phosphate  of 

Lime. 

Price. 

Nitrogen, 
per  cent. 

Value  at 

13s. 
per  unit. 

Phosphate, 
per  cent. 

Valuation 
per  unit. 

Steamed  Bone  Flour. 
Bone  Meal 
Phosphatic  Guano     . 

87s.  6d. 
105s. 

IIOS. 

1.25 
4.0 

2-5 

1 6s.  3d. 

52s. 
32s.  6d. 

59 
44 
58 

IS.  2 Id. 

Is.  2 id. 
IS.  4d. 

We  have  thus  obtained  a  valuation  for  tri-calcium 
phosphate  ranging  from  2s.  per  unit  for  its  water 
soluble  form  in  superphosphate,  down  to  is,  3d.  or  less 
per  unit  in  bones  or  phosphatic  guanos. 

Potassic  fertilisers  do  not  show  a  large  variation,  the 
more  concentrated  and  purified  forms  being  naturally 
somewhat  the  more  costly,  as  follows  : — 

Table  XCIX.— Price  of  Unit  of  Potash. 


Potash, 
per  cent. 

Price. 

Unit  Value. 

Sulphate  of  Potash     . 

Muriate  of  Potash 

Kainit         .... 

48   to   50 
50    „    52 
12    „    13 

2003. 
1 80s. 

47s. 

4s.  id. 
3s.  7d. 
3s.  gd. 

In  dealing  with  mixed  fertilisers  the  nitrogen  is 
generally  the  more  important  element  to  consider,  as 
being    the    most    valuable   and    the   most  subject   to 


XII.] 


UNIT  VALUES 


545 


variations  in  price ;  its  unit  value  is,  therefore,  the 
one  to  be  determined  after  deductions  have  been  made 
for  the  phosphates  and  potash  at  the  rates  quoted 
above.  For  example,  in  the  fish,  meat,  and  oil  cake 
residues  the  phosphates  are  all  of  much  the  same  order 
of  solubility  and  may  be  valued  at  the  same  rates,  the 
small  amount  of  potash  present  also  may  be  neglected, 
so  that  the  following  range  of  values  is  obtained  for  the 
nitrogen  : — 

Table  C— Unit  Values  in  Mixed  Fertilisers. 


Price. 

Phosphates. 

Nitrogen. 

Per  cent. 

Value  at 
Is.  3d. 

per  unit. 

Per  cent. 

Cost 
per  unit. 

Fish  Guano,  I 
Fish  Guano,  2 
Meat  Guano,  I 
Meat  Guano,  2 
Dried  Blood   . 
Bone  Meal      . 
Rape  Meal     . 

1 40s. 
120s. 
130s. 

II  OS. 

I90S. 
105s. 

1 1  OS. 

I5-0 
"•5 

9-0 
27-0 

5-0 
44.0 

5-0 

1 8s.  9d. 
14s.  4d. 
IIS.  3d. 
33s.  9d. 

6s.  3d. 
S5S.  od. 

6s.  3d. 

8-0 
6-0 

8-5 
6-0 
12.5 
4-0 
4-5 

15s.  2d. 
17s.  7d. 
14s.  od. 
I2S.  8d. 
14s.  8d. 
I2s.  6d. 
23s.  id. 

The  variation  in  the  price  of  nitrogen  in  these  very 
closely  related  manures  is  therefore  enormous,  and  the 
important  thing  to  realise  is  that  these  variations  do 
not  represent  intrinsic  differences  in  value — i.e.,  greater 
or  less  effectiveness  in  producing  crops — but  are  market 
variations  due  to  temporary  or  local  fluctuations  of 
supply  and  demand.  As  far  as  anyone  knows  the 
nitrogen  and  phosphoric  acid  in  fish  guano  are  exactly 
of  the  same  value  to  the  crop  as  in  meat  guano,  and 
only  a  few  years  ago  they  were  to  be  obtained  much 
more  cheaply  in  fish  guano,  the  present  high  price  of 
which  is  due  to  a  recent  falling  off  in  the  supply,  coupled 
with  a  large  new  demand  from  Japan.     Just  in  the  same 


346  VALUATION  AND  PURCHASE  [chap. 

way,  rape  dust  was  formerly  almost  as  cheap  a  source  of 
nitrogen  as  nitrate  of  soda  and  established  itself  in  the 
favour  of  hop  growers  and  other  farmers,  who  have 
continued  to  demand  it  in  the  face  of  a  falling  supply 
until  the  price  per  unit  of  nitrogen  has  been  forced  up 
to  nearly  double  its  former  level. 

In  Peruvian  guano  the  potash  must  also  be  taken 
into  account,  and  some  of  the  phosphoric  acid  is  water 
soluble,  so  that  a  higher  allowance  must  be  made  on 
that  account. 

When  all  these  allowances  have  been  made,  it  will 
be  found  that  the  unit  value  of  either  nitrogen  or 
phosphoric  acid  shows  considerable  variation  in  passing 
from  one  fertiliser  to  another,  and  that  the  relative 
position  fluctuates  from  time  to  time.  Even  in 
fertilisers  so  similar  in  their  use  as  nitrate  of  soda 
and  sulphate  of  ammonia  the  unit  of  nitrogen  rarely 
possesses  the  same  price ;  sometimes  one  and  some- 
times the  other  is  the  cheaper,  the  changes  being 
determined  by  factors  of  supply  and  demand  outside 
the  fertiliser  market,  or  by  the  operations  of  the  com- 
binations controlling  the  production  and  sale  of  each 
commodity.  Furthermore,  in  comparing  the  price  of 
the  unit  of  nitrogen  generally,  it  is  not  as  might  be 
expected  at  its  highest  in  the  most  active  fertilisers 
such  as  nitrate  of  soda,  in  which  form  experiments  have 
shown  it  to  be  most  available  to  the  crop.  On  the 
contrary  the  experience  of  the  market  shows  that 
farmers  are  willing  to  pay  more  per  unit  for  nitrogen 
in  organic  than  in  inorganic  combinations,  thus  in- 
directly bringing  into  the  account  the  value  of  the 
organic  matter  in  maintaining  the  texture  of  the  soil. 
The  prepossession  arising  from  an  old  experience  of 
the  well-balanced  nature  of  the  manure  and  its  safety 
under  almost  any  conditions  also  counts  in  the  farmer's 


XII.]  CHOICE  OF  FERTILISERS  347 

estimation  of  a  fertiliser ;  for  example,  the  Peruvian 
guanos  have  been  favourably  known  for  so  long 
that  they  always  command  the  highest  unit  value. 
Unmixed  fertilisers,  which  require  combining  by  the 
farmer  and  so  demand  more  knowledge  in  their  use, 
are  generally  the  cheaper  ;  and  as  a  rule,  little  attention 
is  paid  to  the  imperfect  availability  of  the  slow-acting 
forms  of  nitrogen,  only  the  shoddies  show  any  such 
lowering  of  the  unit  value  as  would  compensate  for 
their  low  availability. 

It  is  impossible,  in  fact,  to  reduce  all  fertilisers  to  a 
common  basis  and  choose  among  them  simply  accord- 
ing to  the  unit  value ;  the  wheat  grower  who  wants  a 
nitrogenous  top  dressing  must  choose  between  nitrate 
of  soda,  sulphate  of  ammonia,  and  soot,  to  which 
nitrate  of  lime  and  cyanamide  may  nowadays  be  added  ; 
the  hop  grower  requiring  an  all-round  spring  fertiliser 
would  not  get  the  quality  of  growth  from  a  mixture 
of  superphosphate  and  sulphate  of  ammonia  that 
is  equivalent  in  nitrogen  and  phosphoric  acid  to 
the  guano  he  usually  employs,  though  a  fertiliser 
made  up  from  the  former  substances  might  be  per- 
fectly satisfactory  to  the  grower  of  barley  or  Swede 
turnips.  The  advantages  of  the  unit  system  of  valua- 
tion really  come  in  the  means  of  comparison  it  affords 
between  fertilisers  of  closely  related  origin  but  different 
composition,  as,  for  example,  between  the  fish  and 
meat  guanos  in  Table  C. ;  it  rarely  happens  but  that  a 
careful  enquiry  will  not  reveal  on  the  market  some  one 
fertiliser  of  the  desired  kind  which  is  considerably 
cheaper  than  the  rest. 

To  this  end  it  is  generally  more  convenient  to  make 
a  slight  change  in  the  form  of  valuation  just  described ; 
instead  of  calculating  out  for  each  manure  the  unit  value 
of  the  constituents,  we  m.ay  take  a  standard  series  of 


348 


VALUATION  AND  PURCHASE 


[chap. 


such  values  and  compare  the  actual  price  with  the 
estimates  formed  on  that  basis.  In  such  comparisons  it 
is  not  necessary  to  know  the  exact  current  unit  value  of 
each  constituent,  as  long  as  a  due  proportion  between 
them  is  preserved,  and  it  will  be  sufficiently  accurate 
to  use  what  are  approximately  the  rates  prevailing  in 
1908,  viz.: — 14s.  per  unit  for  nitrogen,  is.  3d.  per  unit 
of  insoluble  and  2s.  per  unit  of  soluble  phosphate,  and 
4s.  per  unit  of  potash. 

For  example,  fish  and  meat  guanos  were  offered  as 
follows : — 

Table  CI. — Estimated  Value  of  Fertilisers. 


Fish  Guano,  1. 

Fish  Guano,  2. 

Meat  Meal,  3. 

Meat  Meal,  4. 

Nitrogen,  at 

14s. . 
Phosphates, 

at  IS.  3d. . 

Estimated 
value  per  ton 

Sale  price     . 

cent.      Value. 
7i  =  io5s.  od. 

13   =   i6s.  3d. 

cent.        Value. 
10^  =  1473.  od. 

15   —   i8s.  gd. 

c?nt.       Value. 
7  =  98s.  od. 

30  =   37s.  6d. 

l!L       value. 
6   =  84s.  od. 

20  =  25s.  od. 

121S.  3d. 

165s.  gd. 

135s.  6d. 

109s.  od. 

146s.  3d. 

19OS.  od. 

127s.  6d. 

115s.  od. 

Clearly,  among  these  manures  No.  3  is  much  the 
cheapest  fertiliser,  while  No.  i  is  exceptionally  dear; 
unless  there  was  something  wrong  with  the  mechanical 
condition  of  No.  3  there  is  nothing  in  the  relative 
nature  of  the  fertilisers  to  prevent  the  farmer  taking 
advantage  of  its  lower  cost. 

The  example  just  quoted,  which  was  derived  from 
actual  experience,  shows  the  importance  to  the  farmer 
of  a  careful  consideration  of  the  analysis  of  fertilisers  on 
sale ;  too  much  stress  cannot  be  laid  on  the  necessity  of 
conducting  all  transactions  regarding  fertilisers  on  such 


XII.]  SALE  OF  FERTILISERS  349 

a  basis  of  exact  knowledge,  especially  as  the  farmer  has 
no  difficulty  in  obtaining  the  analyses  beforehand  or  in 
checking  the  results  on  delivery.  The  trade  in  fertilisers 
is  regulated  by  the  Fertilisers  and  Feeding  Stuffs  Act 
of  1906,  according  to  which  "  Every  person  who  sells  for 
use  as  a  fertiliser  of  the  soil  any  article  which  has  been 
subjected  to  any  artificial  process  in  the  United 
Kingdom,  or  which  has  been  imported  from  abroad,  is 
required  to  give  to  the  purchaser  an  invoice  stating  the 
name  of  the  article  and  what  are  the  respective  per- 
centages (if  any)  of  nitrogen,  soluble  phosphates,  and 
potash  contained  in  the  article,  and  the  invoice  is  to 
have  effect  as  a  warranty  by  the  seller  that  the  actual 
percentages  do  not  differ  from  those  stated  in  the 
invoice  beyond  the  prescribed  limits  of  error." 

Certain  limits  of  error  are  laid  down  for  each  fertiliser 
in  the  regulations  accompanying  the  Act ;  for  instance, 
one  grade  of  superphosphate  is  guaranteed  to  contain 
26  per  cent,  of  phosphates  made  soluble ;  the  warranty 
implied  is  that  the  fertiliser  contains  27  to  25  per  cent, 
and  that  the  purchaser  can  sustain  a  claim  against  a 
vendor  if  the  percentage  has  fallen  below  25  per  cent. 
Vendors  of  manures  are  no  longer  allowed  to  give 
nominal  guarantees  such  as  i  per  cent,  of  nitrogen ; 
any  statements  of  composition,  made  either  verbally  or 
in  a  circular  about  the  fertiliser,  have  all  the  effect  of  a 
warranty. 

Every  county  council  and  county  borough  is  bound 
by  the  Act  to  appoint  an  agricultural  analyst,  who  for 
a  fee  (generally  small)  must  analyse  and  report  on 
samples  sent  to  him,  provided  these  samples  have  been 
taken  within  ten  days  of  the  receipt  of  the  fertiliser  or 
of  the  invoice.  The  purchaser  must  supply  a  copy  of 
the  invoice  to  the  analyst,  but  may  omit  therefrom  the 
name  of  the  vendor.     The  samples  for  analysis  must,  of 


3SO  VALUATION  AND  PURCHASE  [chap. 

course,  be  taken  with  great  care;  an  official  sampler 
can  be  called  in,  and  this  will  be  the  wisest  course  to 
follow  when  the  purchaser  has  any  reason  to  suspect 
fraud.  When  the  farmer  samples  himself  he  must 
select  a  certain  number  of- bags,  two  for  the  first  ton  in 
the  consignment  and  one  more  for  each  other  ton  up  to 
ten  bags,  empty  the  contents  of  each  on  to  a  clean  dry 
floor,  work  it  up  and  set  aside  a  spadeful  from  each, 
either  separately  or  one  after  the  other.  These 
spadefuls  must  then  be  thoroughly  mixed,  all  lumps 
broken  down,  and  4  to  6  lb.  taken  out  for  the  sample 
for  analysis.  It  is  never  right  merely  to  open  the  bags 
and  take  out  a  spadeful  from  the  mouth  of  each ;  most 
fertilisers,  especially  heavy  powders  like  basic  slag,  will 
show  considerable  differences  between  top  and  bottom 
of  a  bag  which  has  been  in  transit  for  some  time.  The 
sample  as  soon  as  taken  should  be  put  in  a  clean  dry 
bottle  or  jar,  and  either  corked  or  fastened  up  with  a 
bladder  or  other  waterproof  packing  ;  it  must  never  be 
allowed  to  lie  about  in  a  package  or  tin  to  gain  or  lose 
moisture. 

Now  that  every  farmer  in  the  country  can  so  readily 
and  cheaply  obtain  an  analysis  of  any  fertiliser  he 
purchases,  for  besides  the  county  agricultural  analyst 
most  of  the  large  agricultural  societies  have  retained  an 
analyst  for  the  assistance  of  their  members  and  the 
agricultural  colleges  also  undertake  analyses  for  the 
farmers  resident  within  the  area  they  serve,  he  ought 
to  get  analyses  made  of  every  purchase  of  certain 
classes  of  fertiliser,  if  he  has  any  regard  to  the 
economical  conduct  of  his  business.  While  it  is  true 
that  with  very  {q^n  exceptions  the  manufacturers  and 
vendors  of  fertilisers  are  strictly  honest  and  only  wish 
to  supply  the  farmer  with  the  material  they  have 
undertaken  to  sell,  still  a  great   number   of  fertilisers 


XII.]  IMPORTANCE  OF  ANALYSIS  351 

are,  from  their  mode  of  origin,  subject  to  variations  of 
composition  which  may  escape  the  notice  of  the  vendor 
himself.  As  regards  the  pure  unmixed  fertilisers, 
standard  articles  made  on  an  enormous  scale,  such 
as  nitrate  of  soda,  sulphate  of  ammonia,  superphos- 
phate, kainit,  and  sulphate  of  potash,  any  farmer 
dealing  with  a  reputable  firm  may  count  on  getting 
what  he  pays  for,  because  these  materials  do  not  vary 
in  composition  except  they  have  been  deliberately 
falsified  after  they  have  left  the  wholesale  hands. 
But  with  basic  slag,  guanos,  fish,  meat,  and  bone 
compounds,  so  many  different  samples  exist  of  varying 
composition,  and  so  easily  may  even  a  single  cargo 
show  differences  in  passing  from  one  part  to  another, 
that  the  farmer  will  be  always  wise  to  check  his 
purchases  by  an  analysis,  not  of  course  of  the  sample 
that  may  be  submitted  to  him  before  purchase,  but  of 
the  consignment  on  arrival. 

The  farmer  should  buy  his  fertiliser  on  the  strength 
of  the  analysis  or  guarantee  which  he  must  get  from  the 
vendor  before  he  gives  his  order,  and  on  which  he 
should  work  out  a  valuation  by  the  method  described 
earlier  in  the  chapter ;  he  must  then  be  careful  to  see 
that  the  invoice  agrees  with  the  guarantee  on  which  he 
bought,  and  check  the  invoice  by  getting  an  analysis 
made  of  a  sample  drawn  from  the  bulk  delivered.  But 
in  both  his  own  interests  and  those  of  the  vendor  the 
farmer  must  take  some  trouble  over  the  sampling;  a 
good  many  of  the  disputes  that  arise  between  the  two 
parties  are  due  to  careless  sampling  or  to  the  storage 
of  the  sample  afterwards  where  it  can  lose  or  gain 
moisture. 

In  order  to  exercise  to  the  full  his  power  of  buying 
in  the  cheapest  market  prevailing,  it  is  clearly  necessary 
for  the  farmer  to  know  with  some  exactitude  the  kind 


352  VALUATION  AND  PURCHASE  [chap. 

of  fertiliser  he  wants  for  the  crop  in  question,  so  that  he 
can  compound  the  available  materials  in  the  right  propor- 
tions and  not  be  dependent  upon  the  much  more  limited 
range  of  fertilisers  already  mixed  by  the  manufacturer. 
For  example,  every  merchant's  catalogue  will  show 
examples  of  turnip  manures,  barley  manures,  mangold 
or  grass  manures,  containing  such  mixtures  of  nitrogen, 
phosphoric  acid,  and  potash  as  experience  has  shown  to 
be  generally  suitable  to  the  crops  in  question.  In  such 
cases  the  farmer  gets  the  advantage  of  the  knowlege  of 
the  merchant  and  also  obtains  a  carefully  mixed 
fertiliser  of  even  composition  throughout,  which  can 
be  distributed  without  further  trouble.  Such  mixtures, 
however,  can  only  represent  a  certain  average  adapta- 
bility to  the  crop  and  cannot  take  into  account  either 
the  particular  kind  of  land  or  the  condition  it  has  been 
left  in  by  previous  cropping.  The  farmer  who  has 
really  made  himself  acquainted  with  the  theory  of 
manuring  and  with  the  special  conditions  of  his  own 
land  can  always  manure  both  more  cheaply  and 
more  effectively  by  purchasing  unmixed  fertilisers. 
These  he  must  either  sow  separately,  or  by  paying 
a  little  extra  to  the  merchant  he  may  get  made 
up  whatever  mixture  he  desires  before  delivery. 
It  should  not,  indeed,  be  a  matter  of  any  difficulty  to 
make  up  a  sufficiently  accurate  mixture  on  the  farm 
itself,  all  that  is  necessary  being  a  suitable  weighing 
machine  and  a  floor  with  a  space  cemented  or  paved,  on 
which  lumps  can  be  crushed.  The  heaps  of  separate 
manures  should  be  weighed  out  and  thrown  into  a 
common  heap  by  alternate  shovelfuls ;  the  mixture  should 
be  then  passed  through  a  half-inch  screen  and  the  lumps 
broken  down  with  a  wooden  rammer  or  the  back  of  a 
shovel,  the  resulting  heap  being  cast  down  and  remade 
two  or  three  times  until  it  is  uniform  in  appearance. 


XII.]  INCOMPATIBLE  MANURES  353 

It  must  be  remembered  that  certain  fertilisers 
cannot  be  mixed  together  without  setting  up  reactions 
which  are  either  wasteful  or  render  the  mixture  difficult 
to  work.  Basic  slag  and  basic  superphosphate  cannot 
be  mixed  with  sulphate  of  ammonia  or  guano  or  any 
other  fertiliser  containing  ammonium  salts,  because  the 
caustic  lime  reacts  with  the  ammonium  salts  and  sets 
free  ammonia,  which  escapes  as  a  gas.  Superphosphates 
cannot  long  remain  mixed  with  nitrate  of  soda  without 
setting  free  a  certain  amount  of  nitric  acid,  which  is 
both  wasteful  and  injurious  to  anyone  handling  the 
mixture.  It  is,  however,  safe  enough  to  make  up  the 
mixture  and  sow  it  straight  away ;  the  nitric  acid  only 
begins  to  be  in  evidence  when  the  mixture  is  left  in  a 
heap  or  in  bags  overnight,  or  when  it  is  sown  from  a 
machine  which  has  some  moving  part  working  in  the 
manure.  Most  mixtures  containing  superphosphate 
will  turn  into  a  paste  round  machine  parts  working  in 
the  material.  Kainit  and  superphosphate  will  also 
begin  to  set  free  hydrochloric  acid  if  they  are  left  long 
together. 

Superphosphate,  either  mineral  or  bone,  can  be 
safely  mixed  with  sulphate  of  ammonia  or  guano  or 
any  of  the  fish  or  meat  compounds,  but  the  only 
nitrogenous  fertiliser  that  can  properly  go  with  basic 
slag  is  nitrate  of  soda.  In  any  case,  however,  these 
latter  are  better  sown  separately  because  they  differ  so 
much  in  density  and  fineness  that  the  mixture  would 
separate  very  much  in  sowing ;  very  rarely,  indeed, 
would  anyone  want  to  sow  them  at  the  same  time.  Of 
course  lime,  like  basic  slag,  should  never  be  mixed  with 
sulphate  of  ammonia  or  any  of  the  guanos  or  organic 
nitrogen  fertilisers. 

Under  ordinary  conditions  of  farming,  however,  very 
little    mixing    will    be    required,   partly    because    the 

z 


354  '  VALUATION  AND  PURCHASE  [chap. 

manures  are  adjusted  to  the  various  crops  in  the 
rotation,  and  partly  because  it  is  generally  advisable  to 
apply  the  nitrogenous  fertilisers  as  top  dressings  at  a 
later  period  than  the  phosphatic  or  potassic  manures. 

One  other  question  of  valuation  and  price  comes 
into  play  in  connection  with  fertilisers,  and  that  is  the 
value  of  the  residues  left  behind  in  the  soil  after  one  or 
more  crops  have  been  grown.  The  provisions  of  the 
Agricultural  Holdings  Act  of  1900  award  the  tenant 
compensation  for  any  unexhausted  fertility  he  has 
brought  to  and  leaves  behind  on  the  holding.  A 
tenant,  for  example,  who  has  given  his  grass  land  a 
dressing  of  10  cwts,  per  acre  of  basic  slag  and  then 
leaves  his  farm  within  the  following  two  years  will  by 
no  means  have  reaped  the  full  benefit  the  land  has 
derived  from  its  treatment.  On  the  other  hand,  a 
tenant  who  has  used  nitrate  of  soda  to  grow  his  last 
crop  of  oats  or  wheat,  and  then  sells  the  grain  pro- 
duced, will  have  obtained  all  that  the  manure  can 
return ;  no  nitrogen  will  be  left  behind  in  the  soil  for 
the  benefit  of  the  succeeding  tenant. 

It  is  thus  necessary  to  consider  each  fertiliser 
separately  and  attach  some  value  to  the  residue  left 
behind  after  one  or  two  crops  have  been  grown  since 
its  application.  It  cannot,  however,  be  said  that  proper 
data  exist  for  the  compilation  of  such  a  scale  of  com- 
pensation ;  it  is  not  sufficient  to  estimate  what  propor- 
tion of  the  fertilising  materials  that  have  been  applied 
the  crop  may  be  expected  to  remove,  and  then  assume 
that  the  remainder  is  available  for  future  crops. 
Experiments  already  quoted  will  have  served  to 
show  that  residues  of  slow-acting  fertilisers,  such  as 
farmyard  manures  and  shoddy,  are  very  far  from  being 
wholly  recovered  even  after  such  long  intervals  of  time 
as  would  render  any  compensation  quite   out   of  the 


XII.]  UNEXHAUSTED  MANURES-COMPENSATION  355 

question.  To  a  certain  extent,  again,  the  value  of  the 
residue  left  by  a  particular  fertiliser  will  be  determined 
by  the  nature  of  the  land  and  the  crop  to  which  it  has 
been  applied  ;  kainit  applied  to  heavy  clay  land  would 
not  add  to  the  value  of  the  land,  but  on  the  other  hand 
the  benefit  derived  from  the  application  of  fertilisers  to 
grazing  land  is  largely  cumulative,  depending  upon  the 
change  it  effects  in  the  botanical  composition  and 
quality  of  the  herbage,  so  that  the  benefit  may  be 
greater  at  the  end  of  the  third  or  fourth  year  after 
application  than  earlier.  Certainly  no  a  priori  rules  for 
compensation  based  upon  purely  theoretical  considera- 
tions can  be  laid  down ;  any  scale  of  compensation  must  be 
based  upon  experiments  only  and  must  always  be  con- 
sidered as  approximate  and  subject  to  revision  according 
to  the  particular  conditions  of  soil  and  cropping. 

Experiments  instituted  at  Rothamsted  to  provide 
data  for  drawing  up  such  a  scale  have  not  progressed 
far  enough  to  eliminate  the  experimental  error  that 
occurs  in  dealing  with  such  small  quantities  as  are 
involved  in  the  residual  effects  of  most  fertilisers  after 
one  or  two  crops  have  been  grown.  The  crude  practice 
adopted  by  many  valuers  of  allowing  to  the  outgoing 
tenant  half  the  cost  of  the  purchased  fertilisers  he  has 
applied  during  the  last  year  of  his  tenancy,  can  find 
little  or  no  justification,  and  in  the  case  of  such  sub- 
stances as  nitrate  of  soda  and  sulphate  of  ammonia  is 
obviously  unjust  to  the  incoming  tenant,  unless  the 
manure  has  been  applied  to  root  crops  which  have  been 
consumed  on  the  farm.  The  whole  subject  is  very 
complex,  and  data  do  not  as  yet  exist  for  constructing 
any  table  that  would  serve  as  a  basis  for  valuation,  for 
the  compensation  to  be  awarded  will  always  have  to  be 
decided  on  the  merits  of  each  case  after  due  considera- 
tion of  the  soil  and  other  local  circumstances. 


356  VALUATION  AND  PURCHASE  [chap. 

In  the  somewhat  analogous  case  of  the  compensa- 
tion to  be  paid  to  the  outgoing  tenant  for  the  fertiUty 
he  leaves  on  the  farm  from  foodstuffs  purchased  and 
consumed  during  the  last  years  of  his  tenancy,  it  is 
possible  to  draw  up  a  fairly  satisfactory  scale.  The 
custom  in  many  parts  of  the  country  was,  and  still  is,  to 
allow  the  outgoing  tenant  one-half  of  the  cost  of  the  food- 
stuffs he  had  brought  on  to  the  farm  during  the  last 
year  of  his  tenancy,  but  such  a  system  has  obviously  no 
scientific  basis.  The  price  of  a  given  feeding  stuff  is 
determined  by  its  value  as  food,  not  as  manure ;  oil  or 
fat,  for  example,  is  one  of  the  most  costly  constituents 
of  a  feeding  stuff  and  yet  leaves  no  fertilising  residue 
behind.  Many  foods,  e.g.  maize  and  rice,  consist  mainly 
of  carbohydrates  and  contain  an  unusually  small  pro- 
portion of  nitrogen  and  ash  which  would  wholly  or  in 
part  add  to  the  fertility  of  the  farm.  The  proper  basis 
is  to  begin  by  ascertaining  the  nitrogen,  phosphoric 
acid,  and  potash  contained  in  each  class  of  feeding 
stuff;  an  estimate  can  then  be  formed  of  how  much  of 
each  of  these  is  likely  to  reach  the  manure,  and  a 
valuation  made  of  these  latter  quantities  at  the  current 
rates.  The  difficulty  lies  in  estimating  the  proportion 
in  which  the  fertilising  constituents  will  reach  the 
manure ;  for  example,  it  has  already  been  shown 
(p.  199)  that  of  the  nitrogen  fed  to  an  animal  anything 
up  to  15  per  cent,  will  be  retained  by  the  animal,  and 
of  the  rest  that  is  excreted  as  much  as  one-half  may  be 
lost  in  making  the  dung.  Taking  a  general  average 
from  the  experiments  quoted,  it  will  be  seen  that  about 
one-half  of  the  nitrogen  in  the  food  is  likely  to  find  its 
way  to  the  land  in  the  dung  produced  under  ordinary 
conditions  of  farming.  If  the  manure  is  carelessly 
managed  the  losses  will  be  greater ;  on  the  other 
hand,  if  the   food   is   consumed   directly   on  the  land 


XII.]        MANURE  VALUE  OF  FOOD  RESIDUES         357 


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358  VALUATION  AND  PURCHASE      [chap.  xii. 

the  only  loss  will  be  the  amount  retained  by  the  animal. 
Similarly,  milch  cows  will  retain  more  than  fatting 
bullocks,  young  growing  stock  than  work  horses ;  and 
again,  these  variations  will  be  set  off  by  the  fact  that 
both  milch  cows  and  young  stock  are  largely  fed  on  the 
land. 

Taking  these  and  other  considerations  into  account 
J.  A.  Voelcker  and  the  author  have  constructed  a 
scale  of  compensation  for  purchased  foods,  which  has 
been  largely  adopted  by  valuers  in  practice,  on  the 
following  basis — one-half  the  nitrogen,  three-quarters 
of  the  phosphoric  acid,  and  the  whole  of  the  potash 
in  the  food  consumed  during  the  last  year  of  the 
tenancy  will  be  found  in  the  dung,  while  of  the  food 
consumed  in  the  previous  year  only  one-half  of  these 
latter  values  will  remain  on  the  farm.  Thus  the  figures 
given  in  Table  CI  I.  are  obtained  for  i  ton  of  purchased 
foods. 

A  more  complete  set  of  figures  for  the  foods  in 
general  use  may  be  found  in  /.  Roy.  Ag.  Soc,  1902, 
p.  Ill,  or  in  a  report  published  by  the  Central  Chamber 
of  Agriculture. 

Of  course,  no  such  table  can  hope  to  be  more  than 
an  approximation  to  the  truth ;  as  has  been  indicated 
above,  the  style  of  farming  must  introduce  variations 
special  to  each  case,  nor  can  the  table  take  into  account 
any  bad  management  of  land  or  manure  on  the  part  of 
the  farmer.  The  table  assumes  ordinary  mixed  farming 
and  reasonably  good  management  of  the  dung  heap. 


CHAPTER  XIII 

THE    CONDUCT    OF    EXPERIMENTS    WITH   FERTILISERS 

Magnitude  of  Experimental  Error  involved  in  Field  Experiments 
— Choice  of  Land  for  Field  Experiments — Size  and  Shape  of 
Plots — Machines  for  sowing  Fertilisers — 'Should  Farmers  con- 
duct Experiments  upon  their  own  Land  ? 

The  value  of  any  fertiliser,  new  or  old,  on  any  par- 
ticular soil  can  only  be  settled  by  experiment;  for 
though  it  is  now  possible  to  a  large  extent  to  recognise 
types  of  soil  by  their  analysis  and  predict  their 
behaviour,  because  the  main  outlines  of  the  principles  of 
the  manuring  are  understood,  yet  unknown  factors  will 
often  intervene  and  upset  expectations.  The  proper 
conduct  of  field  experiments  is  therefore  a  matter  of 
considerable  moment,  and  it  is  of  particular  importance 
that  the  degree  of  accuracy  which  may  be  expected 
from  a  series  of  such  trials  should  be  realised  before  any 
scheme  of  experimentation  is  embarked  upon.  One 
often  sees  experiments  so  designed  that  the  differences 
between  the  plots  are  likely  to  be  less  than  the 
experimental  error ;  still  more  often  one  sees  conclu- 
sions drawn  from  differences  between  the  yields  of  the 
plots  that  are  smaller  than  the  experimental  error.  Nor 
must  it  be  supposed  that  by  any  amount  of  care  the 
experimental  error  can  be  got  rid  of;  there  are  various 
ways  by  which  it  may  be  diminished,  but  in  some  form 


36o  EXPERIMENTS  WITH  FERTILISERS      [chap. 

or  other  it  must  exist  in  all  work  involving  measure- 
ments, and  the  only  scientific  method  of  dealing  with  it 
is  to  estimate  its  magnitude  and  to  draw  no  conclu- 
sions from  results  which  are  not  well  outside  that 
magnitude.  For  example,  the  experimental  error  of  a 
field  plot  on  average  soil  and  under  ordinary  farming 
conditions  in  this  country  may  be  taken  as  about  lo 
per  cent. ;  this  means  that  if  the  yield  of  the  standard 
Plot  A  be  taken  as  lOO,  and  another  Plot  B  yields  109, 
while  a  third  C  yields  91,  the  conclusion  cannot  be 
drawn  that  B  is  better  than  A,  and  A  better  than  C, 
because  the  same  variations  in  the  results  might  have 
been  seen  had  the  three  plots  been  treated  exactly 
alike.  Furthermore,  unless  the  real  difference  brought 
about  by  two  different  methods  of  treatment  is  greater 
than  10  per  cent,  it  is  hopeless  to  expect  to  reveal 
the  difference  at  all  by  a  single  pair  of  experimental 
plots. 

These  points  may  be  illustrated  by  actual  examples 
drawn  from  the  Rothamsted  experiments,  where  the 
soil  conditions  are  fairly  uniform,  though  by  no  means 
exceptionally  so,  and  the  control  and  management  is 
about  as  good  as  they  can  be  under  ordinary  farming 
conditions. 

On  the  grass  fields  are  two  unmanured  plots  almost 
at  the  two  extremities  of  the  field,  and  taking  a  fifty 
years'  average,  one  of  these  plots  (No.  12)  is  10  per 
cent,  better  than  the  other  (No.  3),  owing  to  some 
fundamental  superiority  of  soil  or  situation.  Table 
cm.  (pp.  361-2)  shows  the  actual  results  given  by  these 
plots  year  by  year,  reduced  to  a  common  standard  by 
taking  the  yield  of  Plot  3  in  each  year  as  100. 

It  will  be  seen  that  though  on  the  average  of  the 
whole  period  Plot  12  is  represented  by  no  when  Plot 
3  is  100,  yet  there  are  twelve  occasions  when  Plot  12 


xni.] 


ACTUAL  AND  RELATIVE   YIELD 


361 


Table  CIII.— Actual  and  Relative  Yield  on  Two   Unmanured 
Grass  Plots.    Rothamsted. 


Yield  of  Hay. 

Relative 

Yield 
of  Plot  12. 
Plot  3  =  100. 

Mean 
of  Plot  12. 

5-year  periods. 

Plot  3. 

Plot  12. 

Lb. 

Lb. 

1856 

2515 

2351 

93 

' 

1857 

2856 

2592 

91 

1858 

2472 

3360 

136 

105 

1859 

2540 

2576 

lOI 

i860 

2760 

2884 

104 

. 

I86I 

2844 

3304 

116 

^ 

1862 

3052 

3424 

112 

1863 

2284 

2844 

125 

121 

1864 

2688 

2808 

104 

1865 

1296 

1932 

149 

. 

1866 

2660 

3012 

113 

A 

1867 

3332 

3048 

91 

1868 

i960 

2676 

137 

128 

1869 

4256 

4352 

102 

1870 

644 

1260 

196 

- 

I87I 

2844 

2960 

104 

1872 

1644 

2252 

137 

1873 

1372 

1804 

131 

121 

1874 

1412 

1642 

116 

1875 

3620 

4232 

117 

1876 

1384 

1599 

116 

1877 

2364 

2165 

92 

1878 

1848 

1832 

99 

108 

1879 

3028 

3157 

104 

1880 

848 

108 1 

127 

I88I 

1480 

1393 

94 

1882 

2524 

2340 

93 

I8S3 

2266 

2322 

102 

102 

1884 

1804 

1996 

III 

1885 

2I0I 

2339 

III 

1886 

2547 

2672 

105 

1887 

I47I 

1330 

90 

1888 

2296 

2298 

100 

96 

1889 

2638 

2383 

90 

X890 

1648 

1565 

95 

362  EXPERIMENTS  WITH  FERTILISERS       [cpiap. 

Table  CI  1 1. — Continued. 


Yield  of  Hay. 

Relative 

Yield 
of  Plot  12. 
Plot  3  =  100. 

Mean 

of  Plot  12. 

5-year  periods. 

Plot  3. 

Plot  12. 

I89I 
1892 

1893 
1894 
1895 

1896 

1897 
1898 
1899 
1900 

1 901 
1902 

1903 
1904 
1905 

Lb. 
2060 
1627 

391 
2685 
1402 

1 144 
1742 
1922 
1342 
1379 

455 
1004 

1509 
2949 
1936 

Lb. 
2422 
2130 

487 
2538 
1399 

1272 

2048 
2256 
1788 
1859 

765 
1200 

1571 
2872 
2297 

118 
131 
125 

95 
100 

III 
118 
117 
133 
135 

168 
119 
104 

97 
119 

114 
123 
121 

Average 

2057 

2254 

no 

yielded  less  than  Plot  3,  while  in  a  single  year  Plot  12 
has  risen  as  high  as  196  per  cent  or  fallen  as  low  as  90 
per  cent,  of  Plot  3. 

Applying  what  is  known  as  the  method  of  least 
squares  to  the  results,  we  can  calculate  that  the  mean 
error  of  a  single  result  is  ±  10  per  cent,  and  that  the 
probable  error  of  the  fifty  years'  mean  is  ±  1-9 
per  cent.  In  other  words.  Plot  12  is  probably  better 
than  Plot  3  by  more  than  8-i,  and  less  than  11-9  per 
cent ;  but  this  superiority  could  never  be  assured  from  a 
single  year's  experiment,  because  it  is  smaller  than  the 
mean  error,  which  is  equal  to  a  lo  per  cent  difference 
between  the  two  plots.  The  probable  error  is  always 
reduced  by  the  number  of  trials ;  if  the  fifty  years  are 


XIII.]  CALCULATION  OF  EXPERIMENTAL  ERROR   363 

collected  into  ten  groups  of  five  years  each,  we  should 
get  the  following  figures  for  Plot  12 — 105,  121,  128,  121, 
108,  102,  96,  114,  123,  121.  In  all  cases  except  one  the 
five  years'  average  of  Plot  12  is  higher  than  that  of  Plot 
3,  and  as  we  can  calculate  as  before  that  the  mean  error 
attached  to  each  figure  is  ±  10-5,  we  could  hardly  have 
concluded  with  confidence  from  any  five  years'  series  that 
Plot  12  was  superior  to  Plot  3,  and  the  extent  of  the 
superiority  would  have  remained  unknown. 

To  take  another  example,  Table  CIV.  represents  the 
results  of  five  years'  experiments  with  different  crops  on 
five  similarly  treated  plots  in  Little  Hoos  field,  reduced 
each  year  to  a  common  standard  by  taking  the  mean  of 
the  five  as  100. 

Table  CIV. 


Plot. 

1904. 

1905. 

1906. 

1907. 

1908. 

Mean  of  5  years. 

A 

98-1 

88-8 

95-8 

86.3 

92-8 

92-3  ±  1-4 

B 

95-8 

92-4 

90-6 

95.1 

94.9 

93-7  i  0-7 

C 

lOl-O 

98.9 

99-2 

102-4 

100-2 

IOO-3  ±  0-6 

D 

1017 

II4-I 

105-0 

109-1 

114-9 

109-0  ±  1-7 

E 

103-4 

105-8 

109-2 

io7'0 

97-3 

104-5  ±  1-4 

Again,  it  will  be  seen  that  the  variations  from  the 
mean  of  the  single  plots  in  any  given  year  are  consider- 
able, the  mean  error  being  ±  7-5,  on  the  assumption  that 
all  the  plots  should  be  exactly  alike.  But  from  the  five- 
year  means  there  would  seem  to  be  some  constant 
difference  in  the  plots,  which  improve  from  A  to  D, 
though  the  superiority  indicated  is  still  of  much  the 
same  magnitude  as  the  experimental  error,  and  that  can 
only  be  reduced  by  continuing  the  trials  over  a  longer 
series  of  years. 

It  will  not  be  necessary  to  go  into  further  detail,  but 
the  above  numbers  illustrate  the  general  principle  that 


364  EXPERIMENTS  WITH  FERTILISERS      [chap. 

as  an  error  of  10  per  cent,  or  so  must  be  expected  in 
the  returns  from  a  single  plot,  this  error  must  be  taken 
into  account  in  the  design  of  any  scheme  of  field 
experiments. 

For  example,  if  trial  plots  are  being  laid  out  and  are 
only  expected  to  continue  a  single  year,  it  would  be 
useless  to  include  among  them  a  comparison  of  sulphate 
of  ammonia  and  nitrate  of  soda  containing  equal 
amounts  of  nitrogen.  There  is  abundant  evidence  that 
the  superiority  of  the  nitrate  of  soda  is  somewhere 
about  10  per  cent. ;  but  as  this  is  no  more  than  the 
expected  experimental  error  a  single  experiment  must 
be  inconclusive.  If  it  is  important  to  settle  for  the 
particular  soil  the  relative  value  of  nitrate  of  soda  and 
sulphate  of  ammonia  more  plots  must  be  given  up  to 
this  one  question ;  at  least  five  would  be  needed,  and 
even  then  there  would  remain  a  possibly  considerable 
error  due  to  the  season. 

This  suggests  that  the  prime  consideration  in 
designing  a  set  of  field  experiments  should  be  to  limit 
the  scheme  strictly  to  certain  definite  questions  which 
can  be  answered  in  the  time  and  space  available. 
There  should  be  no  haphazard  laying-out  of  plots  with 
all  sorts  of  variations  of  manuring ;  the  problems  to  be 
solved  should  be  clearly  thought  out  beforehand ;  it 
will  generally  be  found  that  only  a  very  small  number 
of  problems  can  be  attacked  at  one  time  and  every 
plot  should  be  arranged  to  contribute  to  the  result 
without  the  Introduction  of  any  secondary  or  disturbing 
factors. 

As  to  the  choice  of  land  for  experimental  plots  little 
can  be  done  beyond  exercising  ordinary  discretion  in 
selecting  a  field  which  promises  to  be  uniform.  The 
geological  drift  map  should  be  consulted,  and  places 
marked  by  thin  patches  of  drift  or  on  the  boundaries  of 


XIII.]       CHOICE  OF  LAND  FOR  FIELD  PILOTS  365 

one  or  more  outcrops  should  be  avoided  ;  trial  holes 
should  be  sunk  to  see  that  the  depths  of  soil  and  subsoil 
are  fairly  uniform  ;  thin  soils  on  the  chalk  or  limestone 
should  be  avoided,  because  of  the  very  irregular  surface 
of  the  underlying  rock.  Naturally,  sharp  slopes  should  be 
avoided  ;  if  there  is  any  gradient,  the  plots  should  be  laid 
out  to  run  parallel  to  one  another  up  and  down  the  slope, 
so  that  each  plot  shares  both  the  higher  and  the  lower 
levels.  Other  points  will  suggest  themselves  ;  speaking 
generally,  the  opinion  of  an  intelligent  farmer  well 
acquainted  with  the  land  is  the  most  valuable  guide. 
It  has  been  suggested  to  weigh  up  a  number  of  areas 
when  the  field  is  in  ordinary  crop,  but,  as  indicated  above, 
the  normal  variations  are  so  great  that  several  years  of 
such  trials  would  be  required  to  arrive  at  any  exact 
conclusion.  The  condition  of  the  land  is  equally  im- 
portant ,  land  in  high  condition  should  be  avoided,  since 
for  some  years  at  least  the  effect  of  the  manures  would 
be  swamped  and  all  the  plots  would  give  very  similar 
results.  On  the  other  hand,  bad  land  is  not  desirable,  if 
the  object  is  to  illustrate  the  action  of  fertilisers  and  not 
to  work  out  a  method  of  dealing  with  that  particular 
class  of  land  ;  good  land  in  poor  condition  after  two  or 
more  white  straw  crops  is  the  best.  Care  should  also 
be  taken  to  ascertain  that  the  field  has  not  been  cropped 
or  manured  irregularly  for  the  five  or  six  years  previous 
to  the  trials ;  it  is  astonishing  how  long  the  disturbing 
effect  of  farmyard  manure  or  a  leguminous  crop,  or 
folding  sheep  on  a  portion  only  of  a  field,  will 
persist  and  become  manifest  under  experimental  con- 
ditions. 

The  size  of  experimental  plots  is  a  matter  on  which 
there  are  considerable  differences  of  opinion ;  on  the 
one  hand,  large  plots  smooth  out  the  small  irregularities 
due  to  minor  differences  of  soil  and  drainage,  insect 


366  EXPERIMENTS  WITH  FERTILISERS      [chap. 

attacks,  and  preparation  of  the  land;  errors  of  weighing 
and  measuring  are  also  proportionally  reduced  by  being 
spread  over  the  larger  quantities  involved.  On  the 
other  hand,  the  larger  plots  mean  greater  risks  of 
meeting  with  irregular  patches  of  soil,  and  much  greater 
difficulty  is  experienced  in  getting  the  cultivation  of  all 
the  plots  carried  out  under  uniform  conditions.  It  is  of 
the  first  importance  that  the  whole  of  the  experimental 
land  should  be  worked  on  the  same  day ;  autumn 
ploughings  perhaps  matter  least,  but  spring  ploughings 
and  cultivations,  and  above  all  seeding,  should  be 
carried  through  in  a  single  day.  Otherwise,  if  part  of 
the  land  is  worked  and  left  and  then  the  weather 
changes,  a  considerable  interval  may  elapse  before  the 
operation  can  be  completed,  and  a  new  factor,  often  of 
considerable  magnitude,  is  thus  introduced  into  the 
results.  Sometimes  large  plots  are  necessary  to 
obtain  sufficient  material  for  further  investigation ; 
account,  too,  should  be  taken  of  the  facilities  for 
weighing  up  the  crop ;  if  no  weighbridge  large  enough 
to  take  a  cart  is  available  on  the  farm  it  is  difficult 
to  deal  with  large  areas.  Speaking  generally,  it  may 
be  said  that  with  due  care  a  plot  one-twentieth  of  an 
acre  can  be  made  to  answer  all  ordinary  purposes. 
But  whether  large  or  small  the  most  important  point  is 
to  repeat  the  plots  on  some  regular  system  about  the 
ground,  and  to  have  four  or  five  similar  plots  of  one- 
twentieth  of  an  acre  for  each  treatment  rather  than  one 
of  a  fifth  or  a  quarter  of  an  acre.  In  the  Danish 
experiments  conducted  by  Dr  Sonne  upon  the  relative 
value  of  different  varieties  and  management  of  barley, 
which  may  be  taken  as  the  most  carefully  elaborated 
series  of  field  trials  for  practical  purposes  which  have 
ever  been  carried  out,  the  plots  are  about  ^V  acre  each, 
and   at  any  one  station   there   are   always   four   plots 


Xiii.J  ARRANGEMENT  OF  EXPERIMENTAL  PLOTS  s^; 

receiving  the  same  treatment,  arranged  about  the  field 
as  follows : — 


A 

F 

E 

G 

B 

G 

D 

F 

C 

A 

C 

E 

D 

B 

B 

D 

E 

C 

A 

C 

F 

D 

G 

B 

G 

E 

F 

A 

In  this  way  the  experimental  errors  due  to  inequalities 
of  soil  and  other  accidentals  are  greatly  reduced.  With 
several  stations  repeating  the  same  experiment  in 
different  districts  the  effects  of  soil  may  also  be  largely 
eliminated,  and  in  the  course  of  a  single  season  a  result 
can  be  obtained  which  is  only  subject  to  the  error 
due  to  variations  of  season.  The  shape  of  the  plots 
should  be  long  and  narrow  rather  than  square,  as  this 
tends  to  equalise,  the  soil  conditions,  and  their  breadth 
should  be  chosen  to  give  each  exactly  the  same  number 
of  rows  of  roots  or  corn,  as  the  case  may  be,  a  point 
which  must  be  closely  watched  in  seeding.  When  the 
plots  are  continued  for  more  than  one  season,  some 
method  must  be  adopted  to  mark  their  position  per- 
manently, but  posts  at  the  corners  interfere  with 
cultivation  and  are  often  in  consequence  taken  up  by 
the  labourers.  At  Rothamsted  the  method  adopted  is 
to  set  out  the  plots  initially  in  the  field,  keeping  the 
boundaries  well  away  from  the  hedges  and  trees  (the 
soil  on  the  headlands  of  a  field  is  generally  irregular, 
and  trees  have  a  very  wide-reaching  effect),  and  then 
mark  the  outside  lines  of  the  experimental  area  by 
means  of  stout  posts  painted  white  and  set  in  the 
hedges  round  the  field.      These  being  out  of  the  way 


368  EXPERIMENTS  WITH  FERTILISERS      [cHAP. 

are  subject  to  no  disturbance  until  they  need  renewing 
through  decay,  and  they  afford  sighting  lines  along 
which  lie  the  corners  of  the  actual  plots.  Each  of  these 
corners  is  marked  by  a  stake  or  post  of  creosoted  oak, 
I  foot  long  X  2\  inches  square,  sunk  a  foot  below 
the  surface,  so  as  to  be  out  of  the  way  of  the  plough  or 
any  other  cultivating  tools.  When  the  time  comes  for 
setting  out  the  plots  before  sowing  the  manures,  the 
operator  measures  off  along  the  sighting  line  the  known 
distance  to  the  corner  of  the  first  plot  and  then  probes 
the  ground  with  a  pointed  steel  rod  until  he  finds  the 
buried  post,  above  which  he  sets  up  a  temporary  but 
sufficiently  conspicuous  stake.  Proceeding  in  the  same 
way  he  marks  the  corners  of  all  the  plots,  after  which  the 
manures  can  be  sown  and  the  temporary  stakes  removed 
before  the  manures  are  ploughed  or  harrowed  in.  As  a 
rule  it  is  desirable  to  set  out  the  plots  with  paths  or 
dividing  strips  between  ;  division  strips  are  particularly 
necessary  on  arable  land  to  prevent  the  plough  carrying 
manured  soil  from  one  plot  across  on  to  the  next.  Paths 
result  in  a  stimulus, "  the  fallow  effect,"  to  the  outside  row 
whether  of  corn  or  of  roots ;  consequently  each  plot 
must  be  bordered  by  the  same  extent  of  path ;  in  some 
respects  it  would  be  better  to  dispense  with  them,  but 
the  necessity  of  studying  the  plots  during  growth,  and 
often  of  showing  them  to  large  numbers  of  people, 
renders  them  indispensable.  Whatever  divisions  are 
adopted,  it  is  better  to  sow  the  whole  field  and  strike 
out  the  paths  afterwards  by  a  hoe,  care,  of  course,  being 
taken  to  start  the  drills  each  time  at  the  same  distance 
from  the  edge  of  each  plot. 

If  the  plots  are  continued  year  after  year,  it  is 
necessary  to  watch  the  method  of  ploughing;  if  a 
turnwrest  plough  be  used,  the  mould-board  should  be 
set   to  throw  the  furrows  opposite  ways  in   alternate 


XIII.]      CONDUCT  OF  EXPERIMENTAL  PLOTS         369 

ploughings,  otherwise  the  manured  soil  will  gradually 
be  displaced  sideways ;  if  the  plots  are  ploughed  in 
lands  the  furrows  should  be  alternately  gathered  to  and 
cast  away  from  the  middle  of  the  plot,  or  the  manured 
soil  will  be  accumulated  towards  the  middle. 

It  is  best  to  sow  the  manures  (except  the  nitrates 
and  ammonium  salts)  a  week  or  so  before  the  seed  and 
plough  them  in.  For  sowing  the  manures,  one  of  the 
machines  to  be  described  later  is  best ;  hand-sowing 
produces  considerable  irregularities  which  can  only  be 
obviated  by  mixing  the  manure  with  sufficient  ashes  or 
burnt  earth  to  make  up  a  bulk  of  10  or  12  cwts.  per 
acre  and  sowing  the  mixture  in  three  successive  opera- 
tions. Calm  weather  must  be  chosen  for  sowing  the 
manures ;  many  fertilisers  blow  considerably  if  there  is 
the  least  wind  stirring ;  generally  a  few  still  hours  may 
be  secured  in  the  early  morning. 

It  will  often  be  necessary,  indeed  always  when  the 
manures  are  sown  broadcast  by  hand,  to  have  a  screen  on 
the  edge  of  the  plot  when  sowing  the  strip  which  comes 
up  to  this  edge.  At  Rothamsted  a  canvas-covered 
screen  16  feet  long  x  4  feet  3  inches  high  is  carried 
along  the  edge  parallel  with  the  machine  or  man  sow- 
ing. After  sowing,  the  usual  operations  of  cultivation 
are  carried  out,  but  rather  more  care  than  usual  should 
be  given  to  the  singling  of  root  crops,  so  as  to  obtain  a 
uniformly  set  out  plant  Gaps  and  misses  can,  on  some 
soils,  be  repaired  by  transplanting  at  this  stage,  but  it 
is  not  always  desirable  to  do  so,  because  one  of  the 
properties  of  the  manure  under  examination  may  be  to 
increase  or  diminish  the  tendency  to  lose  plant  In  all 
experiments  with  root  crops  the  actual  number  of 
plants  on  the  plot  should  be  counted  before  harvest 
and  recorded,  as  the  figures  often  afford  a  means  of 
criticising  the  weight  results,  and  of  estimating  the  effect 

2  A 


370  EXPERIMENTS  WITH  FERTILISERS      [chap. 

of  the  manures  upon  the  constitution  of  the  plant.  At 
harvest-time  cereal  plots  can  either  be  cut  by  scythe  or 
a  small  reaping-machine  ;  if  the  plots  are  large  and  the 
paths  wide,  an  ordinary  binder  can  be  employed,  as  is 
done  on  the  Broadbalk  vvheatfield  at  Rothamsted.  As 
the  sheaves  are  tied  they  must  all  be  gathered  on  to 
the  plot  from  which  they  were  cut,  and  a  distinguishing 
label  may  also  be  tied  to  each,  especially  if  the  plots  are 
small.  In  some  cases  threshing  is  done  in  the  field,  but 
generally  in  the  United  Kingdom  it  will  be  necessary 
to  carry  the  unthreshed  sheaves  to  a  rick  or  preferably 
a  barn.  To  keep  the  produce  of  each  plot  separate 
until  threshing  time,  a  number  of  squares  of  thin 
canvas  should  be  prepared,  of  a  fabric  sufficiently  open 
to  allow  of  the  freest  ventilation  but  not  the  passage  of 
any  shed  corn.  The  bottom  of  the  stack  should  begin 
with  some  non-experimental  corn  over  which  one  of  the 
canvas  squares  is  thrown,  followed  by  the  produce  of  one 
plot  together  with  two  wooden  tallies  by  which  it  can 
be  identified.  Another  cloth  is  then  spread  before  the 
produce  of  the  next  plot  is  stacked,  and  so  on  with  the 
other  plots.  Threshing  may  be  done  with  a  special 
machine,  but  the  ordinary  travelling  steam-thresher,  if 
of  modern  construction,  will  do  all  that  is  required ;  at 
the  end  of  each  run  the  screens  must  be  removed  and 
a  little  of  the  straw  again  put  through  the  machine, 
so  as  to  work  out  all  the  grain,  the  last  pint  or  so  of 
which  must  be  extracted  by  hand  from  the  hopper. 
The  grain  should  be  measured  out  bushel  by  bushel,  and 
every  bushel  weighed  and  recorded  ;  the  tail  corn  should 
be  weighed  as  a  whole ;  the  straw  and  cavings  should 
also  be  weighed.  Hay  is  best  weighed  ar»  it  leaves 
the  field  on  the  way  to  the  stack,  and  a^  different 
manures  are  liable  to  lead  to  different  rates  of  drying, 
it  is  well  to  take  a  weighed  sample  from  each  plot  of 


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XIII.]  THE  SOWING  OF  FERTILISERS  371 

the  hay  as  carted,  and  preserve  it  for  a  dry-matter 
determination  in  the  laboratory. 

In  dealing  with  root  crops  it  is  found  convenient  to 
cut  the  tops  off  and  weigh  them  in  large  baskets  in  the 
field ;  the  roots  themselves  are  carted  off  to  the  weigh- 
bridge. Whatever  the  crop,  the  whole  produce  of  the 
plot  should  be  weighed ;  to  cut  out  and  weigh  a  small 
area  introduces  a  fatal  source  of  error — the  selection 
of  the  area.  There  are  a  number  of  other  precautions 
to  take  which  cannot  be  here  enumerated,  but  speaking 
generally,  the  original  records  should  be  as  full  of  detail 
as  possible ;  forms  for  the  entries  should  be  drawn  up 
beforehand  in  such  a  fashion  that  there  is  a  place  for 
every  figure  obtained  in  the  work  without  any  additions 
or  subtractions,  and  all  this  original  material  should  be 
preserved  untouched. 

In  the  use  of  fertilisers,  whether  for  experimental 
purposes  or  in  practical  farming,  it  is  very  important  to 
get  them  distributed  evenly  on  the  land ;  nothing  is 
more  common  in  a  hay  or  cereal  crop  where  nitrate  of 
soda  has  been  used  as  a  top  dressing  than  to  see  regular 
waves  of  a  darker  green  and  stronger  growth  than  the 
bulk  of  the  crop,  representing  the  places  where  the 
fertiliser  fell  from  the  sweep  of  the  sower's  arm.  With 
other  manures  the  irregularity  is  not  so  evident,  partly 
because  they  are  often  sown  before  the  final  working  of 
the  ground,  and  partly  because  they  have  not  the 
striking  effect  upon  the  colour  and  vegetative  develop- 
ment of  the  crop  that  nitrate  of  soda  has.  But  if 
artificial  manures  are  to  be  sown  evenly  by  hand,  it  is 
necessary  to  mix  them  with  a  much  greater  bulk  of 
burnt  earth  or  ashes  and  to  go  over  the  land  more  than 
once ;  better  and  quicker  work  will  always  be  done  by 
a  machine  if  there  is  enough  work  of  the  kind  on  the 
farm  to  justify  its  purchase.     Some  fertilisers,  basic  slag 


372  EXPERIMENTS  WITH  FERTILISERS      [chap. 

and  ground  lime  in  particular,  are  unpleasant  and  even 
dangerous  to  sow  by  hand.  There  are  a  number  of 
different  types  of  machine  on  the  market,  and  all  will 
do  good  work  with  unmixed  dry  fertilisers,  though  some 
fail  to  do  so  with  mixed  manures.  With  a  mixture 
containing  superphosphate,  or  still  more  so  dissolved 
bones,  any  machine  which  possesses  moving  parts 
working  in  the  manure  will  be  sure  to  cause  the  forma- 
tion of  a  paste  which  eventually  clogs  up  the  machine 
and  puts  it  out  of  action.  Whenever  a  farmer  expects 
to  sow  mixtures,  he  must  be  careful  to  get  a  machine 
of  which  no  part  in  contact  with  the  manure  is  actively 
moving. 

At  the  Rothamsted  experiment  station  a  machine 
made  by  Coultas,  of  Grantham,  has  been  in  regular  use 
for  some  time,  and  answers  admirably.  The  principle 
upon  which  the  machine  works  will  be  gathered  from 
the  diagrams.  Fig.  6,  which  show  a  section  through 
the  box  0  n,Z  ft.  or  lo  ft.  6  ins.  long,  which  contains  the 
manure.  The  manure  is  thrown  over  the  lip  of  n  by 
the  revolving  spindle  m,  running  the  whole  length  of 
the  box,  and  furnished  with  a  series  of  radial  arms 
which  dip  in  the  manure  and  toss  it  over  the  lip.  As 
the  machine  travels  the  bottom  and  side  o  of  the 
manure  box  lift,  being  driven  by  the  rack  and  pinion 
k  and  /,  which  are  geared  to  the  wheels  of  the  machine  *. 
the  side  n  of  the  box,  however,  remains  stationary. 
The  spindle  is  also  geared  to  the  wheels  of  the  machine,  ■ 
and  the  rate  at  which  it  revolves,  and  therefore  the  rate 
at  which  manure  is  delivered,  can  be  varied  by  changing 
the  gear  wheels.  After  it  is  tipped  over  the  lip  of  «, 
the  manure  falls  through  a  closed  channel  and  can  be 
delivered  only  a  few  inches  from  the  ground,  so  as  to 
avoid  blowing.  It  will  thus  be  seen  that  this  machine 
fulfils  the  great  desideratum  of  havmg  no  parts  working 


XIII.]     MACHINES  FOR  SOWING  FERTILISERS        373 

in  the  manure,  its  delivery  can  be  stopped  and  started 
sharply,  the  rate  of  sowing  can  be  accurately  gauged, 
and  by  filling  part  of  the  manure  box  with  ashes  only  it 
can  be  made  to  sow  a  narrow  strip  at  the  edge,  should 
the  width  of  the  plot  not  form  a  round  number  of  widths 
of  the  machine ;  thus  it  forms  a  very  suitable  tool  for 
experimental  work.  On  a  very  similar  principle  is  a 
machine  made  by  Messrs  J.  Wallace  &  Sons,  of  Glasgow, 
shown  in  diagrammatic  section  in  Fig.  7.  Here  the 
bottom  of  the  hopper  box  A,  containing  the  manure,  is 
formed  by  a  revolving  drum  B,  which  carries  out  the 
manure  through  the  aperture  regulated  by  the  adjust- 
able slide-plate  N  on  to  the  tray  C,  from  which  it  is 
thrown  so  as  to  fall  on  the  ground  by  the  revolving 
spindle  with  radial  arms,  as  in  the  previous  machine. 
The  rate  of  sowing  is  regulated  by  the  size  of  the 
aperture  controlled  by  N. 

Several  other  makers  construct  machines  akin  in 
principle  to  the  two  described,  in  that  a  revolving 
spindle  with  arms  corresponding  to  the  cups  of  a  seed 
drill  takes  up  the  manure  and  delivers  it ;  they  only 
differ  in  the  way  in  which  the  manure  is  presented  to 
delivery  arms. 

Entirely  different  are  the  machines  constructed  by 
several  makers  on  the  principle  illustrated  in  the  section 
Fig.  8,  derived  from  a  tool  manufactured  by  B.  Reid 
&  Co,,  of  Aberdeen.  Here  the  manure  is  again  con- 
tained in  a  long  hopper,  across  the  bottom  of  which  a 
number  of  endless  chains  move,  actuated  by  a  series  of 
pitch  chain  wheels  geared  to  the  wheels  of  the  machine. 
The  chains  come  out  of  the  box  through  a  narrow  slit 
and  drag  with  them  some  of  the  manure,  which  then 
falls  to  the  ground ;  the  rate  of  sowing  being  regulated 
by  the  gear  wheels  which  actuate  the  spindle  carrying 
all  the   pitch   chain   wheels.     A  more    slowly  moving 


374  EXPERIMENTS  WITH  FERTILISERS      [chap, 

stirrer  within  the  hopper  box  keeps  the  manure  moving 
down  to  the  delivery  chains. 

Again,  on  a  different  principle  are  the  well-known 
broadcast  distributors,  of  which  an  example  made  by 
Messrs  J.  &  R.  Wallace,  of  Castle-Douglas,  is  shown 
in  Fig.  9.  Here  the  manure  is  carried  in  a 
circular  hopper  from  which  it  simply  falls  through 
two  apertures  the  size  of  which  can  be  regulated,  the 
manure  being  kept  in  motion  by  stirrers  within  the 
hopper.  The  manure  is,  however,  not  allowed  to  fall 
direct  to  the  ground,  but  is  intercepted  by  two 
horizontal  discs  with  radial  ribs,  which  are  kept  in 
rapid  revolution  by  gearing  connected  with  the  wheels 
of  the  machine.  As  it  reaches  these  discs  the  manure 
is  flung  rapidly  in  all  directions,  and  so  falls  on  the 
ground  over  a  much  wider  strip  than  the  track  of  the 
machine.  Machines  of  this  type  are  cheap,  light  to 
drive,  and  handy,  and  are  very  convenient  for  sowing 
large  acreages  of  grass  land  with  lime  or  basic  slag. 
The  distribution  is,  however,  not  very  uniform ;  if  the 
manure  is  a  mixture,  the  heavy  particles  are  thrown 
further  than  the  light,  while  the  very  lightest  powders 
are  so  beaten  up  into  a  dust  that  they  float  for  a  con- 
siderable distance,  especially  in  a  wind ;  they  are  thus 
unsuited  for  experimental  purposes  or  any  very  exact 
work. 

The  question  is  often  raised  of  how  far  very  small 
plots,  a  few  yards  square,  cultivated  with  all  the  care 
and  attention  given  by  a  good  gardener  to  his  plants, 
or  even  pots,  can  be  made  to  serve  for  experimental 
work  on  fertilisers,  in  place  of  the  ordinary  field  plots  of 
•^  acre  or  more.  For  demonstration  purposes  they  do 
well  enough,  but  for  investigation  and  local  enquiry  the 
very  care  with  which  the  cultivation  is  carried  out  prevent 
the  variations  induced  by  the  manures  in  the  constitution 


Pitch  Chain 
Wheel 


Rollep 


Roller 


Fig.  8. 


Diagrammatic  Section  of  Manure  Distributor — Endless  Chain 
Feed  Type. 


Fig.  9. — BRo.A.nLAST  Mani  re  Sower  with  Revolving  Discs 

FOR    DiSTRlliUTION. 


XIII.]      EXPERIMENTAL  WORK  B  V  FARMERS  375 

of  the  plants  as  regards  disease,  insect  attacks,  etc.,  and 
in  the  texture  of  the  soil,  from  having  due  weight.  In 
pot  work  the  artificiality  of  the  conditions  is  increased ; 
pot  experiments  are  only  of  value  to  the  investigator  in 
clearing  up  the  earlier  stages  of  an  enquiry  before  the 
applications  to  practice  begin  to  be  considered. 
Deductions  from  pot  experiments  with  regard  to  field 
work  must  be  drawn  with  great  caution  and  always 
regarded  with  suspicion. 

It  will  follow  from  what  has  been  said  about  the  care 
with  which  field  experiments  are  to  be  conducted  and 
the  large  margin  of  error  inherent  in  their  results  even 
under  favourable  conditions,  that  they  are  hardly  to  be 
lightly  entered  upon  by  the  ordinary  busy  farmer,  and 
that  the  advice  so  often  given  to  him  to  work  out  by 
experiment  the  manures  best  suited  to  his  own  farm 
would  really  involve  a  disproportionate  amount  of  work. 
Single-handed  it  will  take  too  long  and  cost  too  much 
to  arrive  at  accurate  results  ;  the  farmer's  experimenting 
should  be  done  as  part  of  a  large  co-operative  local  trial 
designed  to  establish  the  characteristics  of  the  soil  on 
which  he  is  working,  in  regard  to  its  customary  cropping. 
Even  the  usual  habit  of  testing  a  fertiliser  by  leaving 
one  breadth  of  the  field  unmanured  may  often  deceive ; 
concentrated  nitrogenous  manures  easily  show  up  under 
such  conditions,  because  they  affect  the  colour  and  vege- 
tative appearances  of  the  crop  so  markedly ;  basic  slag, 
again,  effects  an  extraordinary  change  in  the  appearance 
of  some  pastures  ;  but,  speaking  generally,  the  effects  of 
the  mineral  and  some  mixed  manures  are  only  to  be 
seen  in  the  yield.  Experience  shows  that  it  is  difficult 
to  detect  by  eye  the  difference  between  two  adjoin- 
ing plots  when  the  yield  of  one  is  20  per  cent,  above 
the  other;  differences  like  10  per  cent,  will  always  go 
unperceived.      In  estimating  the  yield  of  root  crops  the 


376    EXPERIMENTS  WITH  FERTILISERS    [chap.  xiii. 

difficulty  is  increased  by  the  way  the  leaf  takes  the  eye, 
so  that  a  lighter  but  more  leafy  crop,  due  to  a  com- 
parative excess  of  nitrogen,  will  generally  be  set  down 
as  the  heavier. 

In  field  experiments,  as  in  all  other  applications  of 
science  to  agriculture,  the  problems  involved  are  so 
complex,  the  factors  which  intervene  are  so  various  and 
unexpected,  that  the  greatest  rigour  and  technical 
skill  are  called  for  in  the  conduct  of  the  investigation, 
to  be  followed  by  an  even  greater  measure  of  scientific 
caution  in  interpreting  the  results. 


TABLES  FOR  THE  CONVERSION  OF  NITROGEN  INTO 
AMMONIA  AND  PHOSPHORIC  ACID  INTO  TRI- 
CALCIUM   PHOSPHATE. 


Ammonia. 

Nitrogen. 

Nitrogen. 

Ammonia. 

I 

- 

•8235 

I 

= 

1. 214 

2 

= 

1-647 

2 

= 

2.429 

3 

— 

2.471 

3 

= 

3-643 

4 

= 

3-294 

4 

= 

4-857 

5 

= 

4-II8 

5 

= 

6-071 

6 

= 

4.941 

6 

=.- 

7.286 

7 

= 

5-765 

7 

= 

8.500 

8 

= 

6.588 

8 

= 

9.714 

9 

= 

7-412 

9 

=: 

10-93 

Tri-calcium 

Pliosphoric 

Phosphoric 

Tri-calcium 

Phosphate. 

Acid. 

Acid. 

Phosphate. 

I 

= 

•4576 

I 

= 

2.185 

2 

= 

.9152 

2 

= 

4-370 

3 

= 

1-373 

3 

= 

6-556 

4 

= 

1-831 

4 

= 

8-741 

5 

r- 

2-288 

5 

= 

10-926 

6 

= 

2-746 

6 

= 

i3-iir 

7 

— 

3-203 

7 

= 

15-297 

8 

= 

3 -66 1 

8 

= 

17-482 

9 

= 

4-119 

9 

= 

19-667 

Exampk- 

-Reduce  6-43  per 

cent.  Ammonia  and 

35-21 

per  cent. 

cium  Phosphate  to 

Nitrogen  and  Phosphoric  Acid  : 

Tri-calcium 

Phosphoric 

Phosphate. 

Acid. 

6     Ammonia 

=  4-941  Nitrogen 

30 

= 

13-73 

•4 

,, 

=     -329 

5 

= 

2-288 

•03 

II 

=     -025 

•2 

= 

091 

5-295 

01      = 

•005 

16.114 


INDEX 


Absorptive  power  of  litter,  182 
Acetylene  evolved  from  cyanamide, 

Acidity  of  soil,  62,  258,  315 
Adulteration  of  manures,  235 
Agricultural  Holdings  Act,  354 
Air  a  ccespitosa^  256 
Algerian  phosphates,  1 18 
Alkaline,  reaction  in  soil,  55,  321  ; 

salts  required  by  plant,  170,  262 
Ammonia,   absorbed   by    peat-moss 

litter,      183  ;       conversion      into 

nitrogen,   tables  for,  377  ;   fixers 

of,     200  ;    lost    in    dung-making, 

189 
Ammonium    carbonate    from    urea, 

184 
Ammonium  citrate  as  a  solvent,  126, 

132,  143 
Ammonium    salts,     12  ;    action    on 

soil,  62  ;  duration  of,  in  soil,  96  ; 

in  rain,   29  ;   nitrification  of,  60  ; 

versus  nitrate  of  soda,  94 
Ammonium    sulphate,    composition 

of,    58  ;    in   drainage  water,   60  ; 

production  of,   58  ;    retention  of, 

by  soil,  61 
Analysis  of  fertilisers,  349 
Anhydrite,  160 

Antiseptics  in  dung-making,  202 
Apatite,  104,  117,  121 
Artificial  manures,  24 
Australia,  value  of  superphosphate 

in,  140 
Assimilation,  6,  14,  165 
Availability,  of  manures,  91,  97, 145, 

156,  215  ;  of  plant  food,  23,  282 
Azotobacter  chroococcum,  35,  257 

Bacteria,  competing  for  nitro- 
genous manures,  66  ;  denitrif}'- 
ing,  185  ;  humus-forming,  186  ; 
in  soil,  257;  nitrogen  -  fixing, 
II,  32,  34,  273;  putrefactive, 
185 

378 


Bacterial  changes  in  dung-making, 
190 

Barley,  Danish  experiments  on, 
366 ;  effect  of  phosphatic 
manures,  137  ;  effect  of  potassic 
manures,  168  ;  quality,  effect  of 
salt  on,  269 ;  quality  with  nitro- 
genous manures,  66,  81,  308 

Basic  slag,  13,  106,  127,  143,  150; 
composition  of,  129 ;  effect  on 
poor  pastures,  329 

Basic  superphosphate,  133,  152 

Bat  guano,  236 

Beans,  manures  for,  322 

Beijerinck,  35 

Berkeland  -  Eyde,  process  for 
nitrogen  fixation,  43 

Bessemer  process,  127 

Blithe,  W.,  on  manures,  11,  72,  107 

Blood,  dried,  11,  239,  248 

Bone  flour,  145 

Bone  meal,  109,  145,  153  ;  effect  on 
pastures,  331 

Bones,  ii,  103,  106,  145  ;  dissolved, 

"3,  155 
Bonnet,  oxygen  evolved  by  leaves,  6 
Boussingault,     action     of    gypsum, 

267  ;  theory  of  plant  nutrition,  7 
Bracken  fern,  as  indicator  of  lack  of 

lime,  254  ;  as  litter,  182 
Bradley    and     Lovejoy,     electrical 

fixation  of  nitrogen,  42 
Rrown  on  assimilation,  14 

Cabbages,  manures  for,  316 
Cake-fed  dung,  203  ;  cost  of,  227 
Calcium  carbide,  38 
Calcium  carbonate,    250;    removed 

from  soil,  56,  62 
Calcium  cyanamide,  38 
Calcium  phosphates,  104,  142 
Caliche,  46 
Candolle,  293 
Carbide,    combination    of  nitrogen 

with  calcium,  38 


INDEX 


Z79 


Carbohydrates,  denilrification 
favoured  by,  185  ;  potash  required 
for  production  of,  166  ;  required  by 
nitrogen-fixing  organisms,  35,  1 71 

Carbon  bisulphide,  202,  241 

Carbonic  acid,  assimilation  of,  6, 
14  ;  excretion  of,  by  roots,  290  ; 
in  soil  water,  143,  149,  156,  287 

Carnallile,  160 

Cartilage,  108,  154 

Castor  cake,  242,  248 

Catch  crops,  274 

Chalk,  252 

Cellulose,  fermentation  of,  187 

Cercosporium  melonis,  88 

Cheshire,  use  of  bones  in,  ill 

Chinchas  guano,  231 

Chlorophyll,  14,  173 

Christmas  Island,  1 16 

Cinereals,  24 

Citric  acid  solution  as  solvent,  126, 
132,  143,  149,  165 

Cleveland  iron  ore,  127 

Clover,  effect  of  potash  on,  171  ; 
manures  for,  325  ;  value  of  lime 
to,  261  ;  value  of,  in  rotation,  33, 

295,  323 

Clover  sickness,  34,  297,  324 

Club  root,  259 

Coal,  nitrogen  in,  58 

Colour,  relation  to  iron  salts,  270 

Compensation  for  unexhausted 
fertilisers,  354 

Composition  affected  by  manuring 
and  season,  83,  86 

Composition  of,  ash  of  wheat,  264  ; 
average  crops,  22  ;  basic  slag, 
129;  bone  manures,  iii  ;  clover 
ash,  268  ;  excreta,  181  ;  farmyard 
manure,  202  ;  gas  lime,  266 ; 
gases  in  dunghill,  188  ;  guanos, 
248  ;  lime,  255  ;  litter,  182  ; 
London  dung,  207  ;  Peruvian 
guano,  230,  233;  plant,  13; 
sewage  sludges,  247  ;  Stassfurt 
salts,  161 

Condition  in  soil,  lOI,  2I0 

Continuous  growth  of  crops  on  same 
land,  296 

Conservative  systems  of  farming,  302 

Coprolites,  discovery  of,  13,  1 14, 
121,  153 

Corn  marigold,  254 


Cotton,  manures  for,  336 

CoUon  cake,  damaged,  composition 

of,  248 
Cow,  composition  of  excreta  of,  181 
Crookes,    Sir    W.,    on    fixation    of 

nitrogen,  42 
Crust  guanos,  1 16 
Cyanamide,  38 
Czapek,  2gi 

Damaraland  guano,  235,  248 
Danish  barley  experiments,  366 
Daubeny,  114 

Davy,  nutrition  of  plants,  6,  104 
Defiocculation    due    to,   nitrate    of 
soda,  54  ;  potash  salts,  176  ;  salt, 
269 
Defoe,  use  of  the  word  manure,  i 
Deh^rain,  187 
Denitrification,  185,  305 
Diffusion  of  soluble  salts  in  soil,  288 
Digby,  Sir  Kenelm,  on  nitre,  12 
Digestion,  process  of,  179,  191 
Diminishing  returns,  law  of,  283 
Diseases,  fungoid,  86,  174,  216 
Dissolved  bones,  109,  113,  155 
Dissolved  Peruvian  guano,  235 
Dominant  fertilisers,  89,  280 
Dormant  plant  food,  23,  282 
Drainage,  affected  by  farmyard  man- 
ure, 220 ;   water,  composition  of, 
61,  165 
Dried  blood,  239 

Dry  and  wet  seasons,  effect  of  farm- 
yard manure  in,  220  ;  value  of 
potash  salts  in,  175  ;  with  nitro- 
genous manures,  67  ;  with  phos- 
phatic  manures,  137 
Dundonald,  103 
Dung,  cake-fed,  203  ;  definition  of, 

178  ;  value  for  mangolds,  316 
Dyer,  148,  165,  206 

Earth  closet  system,  244 
Egypt,  nitrate  of  soda  deposits  in,  47 
Ellis,  W.,  on  manures,  12,  159,  241 
Epichloe  typhina,  87 
Error  of  experiment,  359 
Estremadura,    phosphates    in,    114, 

117,  123 
Evelyn,    J.,    on    bones,    107  ;    on 

manures,  11  ;  on  nitre,  12 
Excreta,  composition  of,  181,  243 


38o 


INDEX 


Experimenls,  with  fertilisers,  359 ; 
pot,  375 

FAECES,  nature  of,  179,  243 

Farmyard  manure,  changes  during 
making,  189  ;  composition  of,  202, 
205  ;  cost  of  mailing,  224  ;  defini- 
tion, 178  ;  fire-fanged,  191  ;  last- 
ing action  of,  212;  loss  of  nitrogen 
in  making,  192  ;  management  of, 
207;  physical  effects  of,  216; 
slow  availability  of,  215  ;  utilisa- 
tion of,  222,  315,  318,  321  ;  value 
of,  209,  216 

Feathers,  11,  71 

Felspar,  163 

Fermentation,  of  cellulose,  187 ;  of 
urea,  184 

Fertilisers,  compensation  for  residues 
of,  354  ;  experiments  with,  359  ; 
machines  for  sowing,  372  ;  mixed, 
352 ;  required  in  ordinary  farm- 
ing, ,  305 ;  sampling  of,  350 ; 
significance  of  term,  2,  23  ;  valua- 
tion of,  340 

Fertilisers  and  Feeding  Stuffs  Act, 

235>  349 
Fertility,  of  soil,  305  ;  unexhausted, 

354 

Finger-and-toe,  151,  216,  259,  315 

Fire-fanged  manure,  191 

Fish  guano,  236,  248,  345 

Fish  waste,  12,  75,  236 

Five  fingers,  75 

Fixation  of  nitrogen,  by  bacteria, 
32 ;  by  calcium  carbide,  38 ;  by 
electricity,  42  . 

Flocculation  of  soils  by  lime,  255 

Flock  dust,  71 

Florida  phosphates,  1 16 

Folding  of  sheep,  274 

Foods,  fate  of  nitrogen  in,  180; 
manure  value  of,   225,  356 

Foxglove,  254 

Frank  and  Caro,  cyanamide,  38 

Franklin,  Benjamin,  267 

Fray  Bentos  guano,  238 

Fruit,  manures  for,  334 

Function  of,  iron  salts,  270 ;  nitro- 
genous manures,  77  ;  phosj^hatic 
manures,  136;  potassic  manures, 
165  ;  silica  in  plant  nutrition,  271 

Fungi  in  dung,  191 


Fungoid  diseases,  and  lime,  259  ; 
and  nitrogenous  manures,  86 ; 
and  potash  manures,  174;  carried 
by  farmyard  manure,  216 

Garden  manures,  338 

Gases  contained  in  dunghill,  187 

Gas  lime,  254,  262,  265 

(Gilbert,  Rothamsted  experiments,  9 

Grasses,     appearance     of     potash - 

starved,  173  ;  developed  by  nitro- 
genous manures,  65 
Grass  land,  effect  of  lime  on,  259 ; 

effect  of  potash  on,  173  ;  manures 

for,  326  ;  value  of  dung  on,  221 
Greaves,  74,  239,  248 
Green  manuring,  272 
Grinding  of  bones,  107;  of  fertilisers, 

value  of  fine,  150,  154 
Ground  lime,  253 
Guano,    12,    145,    346 ;    bat,    236 ; 

Damaraland,     235  ;     fish,     236 ; 

Ichaboe,    235  ;   meat,  236,   238  ; 

native,     246;    phosphatic,     115, 

145,  152,  229 
Gunpowder  salt,  269 
Gypsum,    106,   113,  124,  160,  262, 

266 ;  as  an  ammonia  fixer,  201  ; 

phosphatic,  134 

Hair,  ii,  71 

Hay,  manures  for,  329 

Hellriegel,  experiments  upon  barley, 

166  ;  growth  and  nitrogen  supply, 

28;  nitrogen-fixing  bacteria,  11 
Henslow,  discovery  of  coprolites,  13, 

121 
High  farming,  301 
Highland  and  Agricultural  Society's 

experiments,  153,  313 
History  of  manuring,  2,  11,  103,  158, 

249 
Holdings  Act,  Agricultural,  354 
Hoofs,  II,  71 

Hop  bine,  composition  of,  181 
Hops,  manures  for,  333  ;  spent,  74 
Horn,  II 

Horse,  composition  of  excreta  of,  181 
Hughes,    F.,   analysis   of  Egyptian 

nitrate  of  soda,  47 
Hughes,  J.,  basic  superphosphate, 

133 
Humboldt,  A.  von,  231 


INDEX 


381 


Humus,  formation  in  dunghill,  186  ; 

in  soil,  value  of,  216,  273 
Hydrogen   evolved  from    dunghill, 

187 

ICHABOE  guano,  235,  248 

Incompatibles,  353 

Ingenhousz,  light  essential  to 
assimilation,  6 

Inoculation  of  soil,  36 

Iron  in  soil,  function  of,  270  ;  sul- 
phate of,  270 

JODlN,  272 

Kainit,  160,  164,  201 

Kalk-stickstoff,  38 

Kellner,  191 

Kelp,  158,  163 

Kiln  dust,  74 

Kirwan,  104 

Knop,  water  cultures,  10 

Kohl  rabi,  manures  for,  316 

Kossowitsch,  292 

Lahn  phosphates,  116 

Law  of,  diminishing  returns,  283  ; 
the  minimum,  282 

Lawes,  manufacture  of  superphos- 
phate, 13.  120  ;  on  turnip  culture, 
138  ;  origin  of  Rothamsted  ex- 
periments, 9  ;  use  of  ammonium 
salts,  12 

Lawns,  manures  for,  338 

Leather,  71 

Leaves,  assimilation  b}-,  6,  14,  168  ; 
stimulated  by  nitrogen,  85 

Leguminous  crops,  manures  for, 
322  ;  plants  and  nitroijen,  10,  32  ; 
effect  of  potash  on,  171 

Leuchstadt,  experiments  at,  192,  202 

Leucite,  163 

Liebig,  on  bones,  104,  107  ;  on 
superphosphate,  I19 ;  silicate 
manures,  272  ;  £Ource  of  plants' 
nitrogen,  9,  1 1  ;  theory  of  plant 
nutrition,  7,  276 ;  use  of  am- 
monium salts,  12 

Lime,  action  of,  on  soil,  63,  249, 
257  ;  ashes,  251  ;  ground,  253  ; 
in  basic  slag,  128,  151 

Limestone,  250 

Limiting  factors  for  growth,  284 


Liquid  manure,  205 

Litter,  composition   of,  181  ;   effect 

of,  on  losses  of  nitrogen,  195 
Lobos  phosphatic  guano,  115 
Lodging,  due  to  excessive  nitrogen, 

Lcihnis,  decomposition  of  cyanamide, 

39 
London  dung,  206 
Lucerne,  manures  for,  325 
Lupins  as  green  manure,  272 

Machines  for  sowing  fertilisers,  372 
Maercker  and  Schneidewind,  192 
Magnesium  salts  in  manures,   163, 

262,  269 
Magnesian  limestone,  251 
Maize,  manures  for,  312 
Malt  dust,  12,  74 
Manganese  salts,  action  of,  271 
Mangolds,  with  increasing  nitrogen, 
29  ;  effect  of  sodium  salts  on,  52  ; 
late  growth  with  nitrate  of  soda, 
66  ;   effect  of  manuring  on  com- 
position, 86  ;   effect  of  manuring 
upon    number,     102  ;     effect     of 
potassic  manures,  168  ;   value  of 
salt  for,  268  ;  manures  for,  316 
Manure,  significance  of  term,  i,  24 
Manure  value  of  foods,  225,  356 
Manures,  compounded,  301 
Manures    for    barley,    308 ;    beans, 
322  ;  cabbages,  316  ;  clover,  324  ; 
cotton,   336  ;  fruit,   334  ;  garden, 
338  ;  grass  land,  326  ;  hops,  333  ; 
lucerne,   325  ;  maize,   312  ;  man- 
golds, 316;    oats,    311;   pasture, 
329;    potatoes,    319;    rye,    312; 
sainfoin,       325  ;      sugar,        336 ; 
Swedes,  312  ;  tea,  337  ;  tobacco, 
337  ;  tropical  crops,  335  ;  vetches, 
326  ;  wheat,  306 
Marl,  249 
Marsh  gas  evolved  from  dunghill, 

187 
Maturity,  accelerated  by  phosphoric 
acid,  136  ;  deferred  by  excess  of 
nitrogen,  78  ;  effect  of  potash  on, 

174 
Meat  guano,  236,  238,  248,  345 
Micrococcus  iirccc,  184 
Mineral  manures,  24  ;   duration  of, 

in  soil,  96 


382 


INDEX 


Minimum,  law  of,  282 
Mixed  fertilisers,  352 
Miinlz  and  Girard,  195 
Murray,  Sir  James,  123 
Mussels,  75 

Mustard,  as  green  manure,  272 
Mustard  seed  in  rape  cake,  240 
Mulch,  farmyard  manure  as  a,  221 

Native  guano,  246 

Night  soil,  244 

Nilson,  134 

Nitrate  of  lime,  44 

Nitrate  of  soda,  12,  307  \  action  on 
soil,  51,  54  ;  compared  with 
ammonium  sulphate,  64,  94  ; 
composition,  49 ;  for  cabbages, 
316 ;  in  Egypt,  47  ;  source  of, 
45  ;  value  of  soda,  53,  170 

Nitrates,  saving  of  soil,  273  ;  soil, 
289 

Nitric  acid  in  rain,  29 

Nitrification,  in  spring,  90  ;  in  wet 
seasons,  67 

Nitrogen,  and  fungoid  diseases,  86  ; 
compounds  of,  in  dung,  206  ; 
contained  in  rain,  29 ;  conver- 
sion into  ammonln,  tables  for, 
377 ;  electrical  fixation  of,  42  ; 
fixation  by  calcium  carbide,  38  ; 
fixed  by  Leguminosas,  1 1  ;  growth 
proportional  to  supply  of,  28  ;  in 
food,  fate  of,  180  ;  in  wheat  grain 
and  flour,  84  ;  losses  by  denitri- 
fication,  185,  305  ;  lost  in  dung- 
making,  192  ;  origin  of  combined, 
30;  recovered  in  crop,  99,  210; 
removed  in  four-course  rotation, 
303 ;  source  of  plants',  9,  26 ; 
value  of  unit,  342 ;  vegetative 
growth  promoted  by,  77 

Nitrolim,  38 

Nodule  organisms,  273 

Nucleo-proteins,  140 

Nutrition,  theories  of,  5-6,  13 

Oats,  manures  for,  31 1 
Oilcake,  12,  240,  242,  345 
Oil  in  manures,  72,  237 
Oospora  scabies^  321 
Organic  manures,  value  of,  94,  lOO 
Organic  matter,  value  of,  in  soils, 
73 


Palissy,  B.,  observationson  manures, 

4 

Pasture,  manures  for,  329 

Peat  moss,  as  litter,  181,  195  ; 
manure,  183 

Peruvian  guano,  12,  115,  229,  248, 
338,  346  ;  dissolved,  235 

Phosphate  rock,  115,  156 

Phosphatic  guano,  115,  152 

Phosphate,  conversion  into  phos- 
phoric acid,  tables  for,  377  ;  of 
iron,  125;  of  lime,  104,  142; 
value  of  unit,  343 

Phosphates,  action  of  lime  on  soil, 
260 ;  required  by  barley,  309 ; 
required  by  turnips,  313 

Phosphatic  gypsum,  134 

Phosphoric  acid,  103,  136  ;  and 
nitrogen  in  plant,  140 ;  conver- 
sion into  phosphate  of  lime,  tables 
for,  377  ;  value  of  unit,  343 

Phosphorus  in  iron,  127 

Photo-synthesis,  15,  169 

Pickering,  298 

Pigs,  composition  of  excreta  of,  181 

Plant  food,  dormant  and  available, 
23  ;  in  soil  and  crop,  21 

Plasmolysis,  18,  50 

Plasmodiophora  brassiccp,  259 

Pliny,  250 

Plots  for  field  experiments,  size  of, 
365 

Poly  halite,  160 

Polzenius,  stickstoff-kalk,  41 

Pot  experiments,  375 

Potash  salts,  13 

Potash,  158  ;  value  of  unit,  344 

Potassium  carbonate,  163  ;  function 
of,  in  nutrition  of  plant,  166 ; 
salts,  retention  by  soil,  164 

Potatoes,  manures  for,  319 

Precipitated  phosphate,  134,  152 

Preservatives  in  dung-making,  200 

Priestley,  discovery  of  assimilation, 
6,  276 

Pugh,  source  of  plant  nitrogen,  9 

Quality  in  produce,  66,   72,  81, 

269,  270,  308,  320 
Quicklime,  250 

Rabbit  hair,  71 
Rags,  II,  72 


INDEX 


383 


Rain,  nitrogen  contained  in,  29 

Rape  dust,  94,  240,  248,  345 

Recovery  of  nitrogen  in  crop,  99, 
210 

Residues  from  manufactories,  67  ; 
compensation  for  manuriai,  354  ; 
duration  of  manuriai,  71,  96,  98, 
212 

Retention  of  fertilisers  by  soil,  148, 
164 

Reverted  phosphate,  106,  126 

Ripening  caused  by  phosphatic 
manures,  136 

Rochdale  manure,  245 

Rock  salt,  159 

Roman  agriculture,  2,  250 

Roots,  development  of,  with  nitro- 
genous manures,  65  ;  effect  of 
phosphatic  manures  on,  139; 
ratio  of,  to  leaf,  85  ;  solvent  action 
of,  290 

Root  system,  importance  of,  280 

Rotations,  32,  293,  301,  319 

Rothamsted,  analysis  of  soil,  20  ; 
experiments,  9,  13,  26,  277,  360; 
grasB  plots  at,  65 

Russell,  dung-making  experiments, 
199  ;  on  heated  soil,  298  ;  com- 
position of  seaweed,  75 

Rye,  manures  for,  312 

Sachs,  272,  290 

Sainfoin,  manures  for,  325 

Sale  of  fertilisers,  349 

Salt,    262,  268,    319;    gunpowder, 

269  ;  nitrate  of,  51 
Sampling  of  fertilisers,  349 
Saussure,  nutrition  of  the  plant,  6, 

17,    276  ;    on  ammonia,    I2  ;    on 

phosphate  of  lime,  104 
Scabby  potatoes,  321 
Schubler,  theory  of  manures,  7 
Schneidewind,  192,  202 
Sclerotinia  disease,  34,  297 
Season,    effect     of,    on    yield     and 

quality,  67,  83 
Seaweed,  75 
Secular    decline    in    yield    of   crops 

grown  continuously,  296 
Selective  action  of  plant,  19 
Senebier,  assimilation,  6,  276 
Sewage,  245  ;  sludge,  246 
Sheep,  composition  of  excreta  of,  181 


Shoddy,  71,  334 

Short  manure,  190,  205 

Sickness  of  land,  297 

Silica,  action  of,  on  plants,  271 

Skin,  12,  71 

Slaked  lime,  251 

Slaughter-house  refuse,  13,  70 

Sodium  perchlorate,  51  j  salts, 
action  of,  53,   170 

Solubility  of  phosphatic  manures, 
143  ;  soil  phosphates,  285 

Soil,  acidity,  62  ;  analysis  of  Rotham- 
sted, 20;  condition  in,  210;  ino- 
culation of,  36 ;  phosphates  in, 
144 ;  temperature,  69 ;  texture 
affected  by  manures,  lOl,  163, 
176,  216,  269,  273;  requiring 
potash  manures,  177 

Somme  phosphates,  116 

Sonne,  Danish  barley  experiments, 
366 

Sorrel,  254 

Soot,  II,  68,  307 

Sprengel,  theory  of  manures,  7 

Spurrey,  254 

Stassfurt  deposits,  13,  159 

Steamed  bone  flour,  109,  145,  1 52 

Stickstoff-kalk,  42 

Stohmann,  water  cultures,  lO 

Straw,  composition  of,  182 

Stimulus  due  to  manganese  salts,  271 

Sugar  cane,  manures  for,  336 

Sulphuric  acid,  as  an  ammonia- 
fixer,  202  ;  in  manures,  74 

Superphosphate,  106,  1 19;  as  an 
ammonia-fixer,  202  ;  retention  by 
soil,  148;  use  of,  150;  value  in 
Australia,   140 

Swede  turnips  and  nitrogenous 
manures,  90,  280,  312 

Surface  tension  of  dung  solutions, 
221 

Sylvinit,  161 

Systems  of  manuring,  300 

Tafla,  47 

Tankage,  238 

Tares  as  green  manure,  272 

Tea,  manures  for,  337 

Temperature  of  soil  raised  by  soot, 

69 
Tetra-basic  phosphate  of  lime,  106, 

131,  143 


3^4 


INDEX 


Texture  of  soil  affected  by  manures, 

loi,  163,  176,  216,  269,  273 
Thaer,  theory  of  plant  nutrition,  5, 

7 
Theories  of,  plant  nutrition,  5-6,  13  ; 

fertiliser  action,  276 
Thomas  and  Gilchrist,  127 
Thomas  phosphate,  129 
Tillering  promoted    by   phosphoric 

acid,  139 
Tobacco,  manures  for,  337 
Top-dressings,  58,  307 
Toxic  substances  excreted  by  plants, 

293 
Transpiration,  18 
Trefoil,  manures  for,  326 
Tropical  crops,  manures  for,  335 
Toll,  theory  of  plant  nutrition,  5 
Tunis  phosphates,  118 
Turnips,  manures  for,  313 

Unexhausted  residues,  compensa- 
tion for,  354 
Unit  system   of   valuing    manures, 

341,  348  .  . 

Urea,    decomposition    of,    184;    in 

guano,  230,  233 
Urine,  nature  of,  179 
Uromyces  betm,  87,  174 

Valuation,  of  farmyard  manure, 
223  ;  of  manures,  73,    lOO,    155, 

340 
Van    Helmont,     theory     of    plant 

nutrition,  5 
Vetches,   as    green    manure,    272 ; 

manures  for,  326 
Ville,  89,  281 
Virgin  soils,  31,  35,  302 
Vitriolised  bones,  109 
Voelcker,  195,  274,  358 

Wagner,  comparison  of  nitrogen- 
ous manures,  97 


Walter  de  Henley's  Husbandries  3 

Warrantry  of  fertilisers,  349 

Waste  products  as  manures,  67 

Water,  effect  of  dung  on  surface 
tension  of,  221  ;  retained  by 
humus  in  soil,  219 

Water  cultures,  10,  16,  55,  277 

Way,  analysis  of  superphosphate, 
124  ;  retention  of  manures  by 
soil,  164 ;  soluble  silicates  as 
manures,  272 

Wet  seasons,  effect  of  farmyard 
manure  in,  220  ;  with  nitrogenous 
manures,  67 ;  with  phosphatic 
manures,  137 ;  with  potash 
manures,  175 

Wheat,  development  of  grain,  142  ; 
effect  of  phosphatic  manures  on, 
139;  habit  of  growth,  89;  manures 
for,  306 ;  nitrogen  in  grain  and 
flour,  84  ;  yield  with  increasing 
nitrogen,  80 

Whitney  and  Cameron,  285 

Wiborg  phosphate,  134 

Wilfarth,  nitrogen  -  fixing  bacteria, 
II 

Woburn,  acidity  of  soil  at,  62  ;  ex- 
periments at,  95,  274 ;  experi- 
ments on  dung-making,  195 ; 
fruit  farm,  298 

Wolff  and  Lehmann,  243 

Wolter  phosphate,  135 

Wood,  dung-making  experiments, 
198 

Wood  ashes,  11,  159,  163 

Wool,  ir,  72 

Worlidge,  107 

Wrightson  and  Munro,  128 

Young,  A.,  on  woollen  rags,  72 ; 
on  bones,  107 

Zeolites  in  soil,  51,  260,  267 


»>RINTED  BY    OLIVER  AND  BOYD,   KDIKBUBGH. 


i 


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